[JRuby] Skip few of the ActiveSupport's inflector test cases

This doesn't affect MRI, JRuby only

[These tests](https://gist.github.com/gaurish/6264679) are failing on JRuby & will keep failing for quite some time as JRuby is missing some functionality(available in MRI) required for these tests to pass. here is the relevant bug report: [UTF-8 to UTF8-MAC Converter Missing ](http://jira.codehaus.org/browse/JRUBY-7194)

Since we know they are failing, why they are failing. it would be a good idea to skip them while we find a workaround or  wait for JRuby to implement the `UTF-8 to UTF8-MAC Converter`  which is not likely to happen soon.  

so is it a good idea to skip these for now?

cc: @arunagw, @guilleiguaran 

#11700