Unset RUBYOPT to avoid Bundler leak platform-specific details

Bundler uses RUBYOPT to ensure child Ruby interpreter used uses
the same Gemfile and interpreter.

This affects the different versions of Ruby during cross-compilation.

Of course, this needs to be solved by rake-compiler, but we can
workaround this issue for the time being.

Author: luislavena

bin/package_win32_fat_binary

@@ -20,4 +20,4 @@ rvm use $base_version
 bundle install
 
 bundle exec rake clean
-bundle exec rake cross native gem RUBY_CC_VERSION=$cc_versions
+bundle exec rake cross native gem RUBY_CC_VERSION=$cc_versions RUBYOPT=