small fix on ruby_version check

The ruby version check could happen before Rails.logger gets intialized
so we cannot assume that Rails.logger is not nil.
Example: https://travis-ci.org/errbit/errbit/jobs/8719703

lib/support/ruby_version.rb

@@ -2,7 +2,7 @@
 # squarm for answers
 def raise_version_error(message)
   puts message
-  Rails.logger.info(message) if defined?(Rails)
+  Rails.logger.info(message) if defined?(Rails) && Rails.logger
   raise
 end