ajb/erector-rails4 — pull request #39 by Sen (2014-11-01 05:54:49+00:00)
Title: ruby syntax error

fix the error when trying to run `rake formbuilder:install:migrations` from formbuilder-rb by my side:

```
/usr/local/var/rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/activesupport-4.1.6/lib/active_support/dependencies.rb:247:in `require': /usr/local/var/rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/gems/erector-rails4-0.2.0/lib/erector/caching.rb:13: syntax error, unexpected modifier_if
dynamic_keys: if options[:needs_keys]
```