Fix #32: Running iridium compile with default config/production.rb fails

When running ```bundle exec iridium compile``` I'm getting the following exception.

```
/Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-pipeline-web-filters-0.7.0/lib/rake-pipeline-web-filters/handlebars_filter.rb:52:in `block in generate_output': undefined method `call' for Iridium::Pipeline::HandlebarsPrecompiler:Class (NoMethodError)
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-pipeline-web-filters-0.7.0/lib/rake-pipeline-web-filters/handlebars_filter.rb:44:in `each'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-pipeline-web-filters-0.7.0/lib/rake-pipeline-web-filters/handlebars_filter.rb:44:in `generate_output'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/filter.rb:218:in `block (3 levels) in generate_rake_tasks'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/file_wrapper.rb:135:in `create'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/filter.rb:218:in `block (2 levels) in generate_rake_tasks'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:227:in `call'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:227:in `block in execute'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:222:in `each'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:222:in `execute'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:166:in `block in invoke_with_call_chain'
	from /Users/stephan/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/monitor.rb:211:in `mon_synchronize'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:159:in `invoke_with_call_chain'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/dynamic_file_task.rb:154:in `invoke_with_call_chain'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/gems/rake-0.9.5/lib/rake/task.rb:152:in `invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/dynamic_file_task.rb:60:in `invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline.rb:328:in `block (2 levels) in invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline.rb:328:in `each'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline.rb:328:in `block in invoke'
	from <internal:prelude>:10:in `synchronize'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline.rb:321:in `invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/project.rb:126:in `each'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/project.rb:126:in `block in invoke'
	from <internal:prelude>:10:in `synchronize'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/rake-pipeline-ae0795842a89/lib/rake-pipeline/project.rb:112:in `invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/iridium-c0c8e6fd5a23/lib/iridium/pipeline.rb:52:in `block in compile'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/iridium-c0c8e6fd5a23/lib/iridium/pipeline.rb:51:in `chdir'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/iridium-c0c8e6fd5a23/lib/iridium/pipeline.rb:51:in `compile'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/iridium-c0c8e6fd5a23/lib/iridium/pipeline/compile_command.rb:11:in `compile'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/task.rb:27:in `run'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/invocation.rb:120:in `invoke_task'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor.rb:344:in `dispatch'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/invocation.rb:109:in `invoke'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor.rb:214:in `block in subcommand'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/task.rb:27:in `run'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/invocation.rb:120:in `invoke_task'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor.rb:344:in `dispatch'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/thor-15eedc90f499/lib/thor/base.rb:434:in `start'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bundler/gems/iridium-c0c8e6fd5a23/bin/iridium:4:in `<top (required)>'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bin/iridium:23:in `load'
	from /Users/stephan/.rvm/gems/ruby-1.9.3-p194/bin/iridium:23:in `<main>'
```