FindRuby.cmake does not set backward compatible RUBY_VENDORLIB_DIR
When the variables set by FindRuby.cmake were renamed to use the module name casing (e672db62). The old variables were aliased in a for loop at the end of FindMake.cmake to make this change backwards compatible. However, a copy-paste error caused the last one (Ruby_VENDORLIB_DIR) to be lost in the backward compatibility aliases, so now RUBY_VENDORLIB_DIR does not work anymore.