changing serverspec dependency to greater than or equal to 0.13.5

Serverspec is at 1.0.0 now, ansiblespec-init won't run. I don't know if >= 1.0.0 is ok, but I'm sending a pull request anyways. :)

```bash
curtis$ ansiblespec-init 
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/dependency.rb:296:in `to_specs': Could not find 'serverspec' (~> 0.13.5) - did find: [serverspec-1.0.0] (Gem::LoadError)
	from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/specification.rb:1196:in `block in activate_dependencies'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/specification.rb:1185:in `each'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/specification.rb:1185:in `activate_dependencies'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/specification.rb:1167:in `activate'
	from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_gem.rb:48:in `gem'
	from /usr/bin/ansiblespec-init:22:in `<main>'
curtis$ gem list | grep serverspec
serverspec (1.0.0)
```