Symbol to String - fix v0.11.13

As of V8 3.24 Symbol API has changed an NewSymbol does not exists anymore (https://code.google.com/p/v8/source/browse/branches/3.24/include/v8.h#1909)
I tried with the new API Symbol::New(isolate, 'char') with no success - btw source code is mentionning that it's an experimental feature.
Changed to String seems to do the job pretty well, is there any reason that would make that to fail?

#27