Capitalized R detection

[ThomDietrich]

Seems like a simple bug:

$ sloc ./*.R
C:\Users\Birke\AppData\Roaming\npm\node_modules\sloc\lib\sloc.js:195
          throw new TypeError("File extension '" + lang + "' is not supported");
          ^

TypeError: File extension 'R' is not supported
    at getCommentExpressions (C:\Users\Birke\AppData\Roaming\npm\node_modules\sloc\lib\sloc.js:195:17)
    at slocModule (C:\Users\Birke\AppData\Roaming\npm\node_modules\sloc\lib\sloc.js:376:31)
    at C:\Users\Birke\AppData\Roaming\npm\node_modules\sloc\lib\cli.js:84:19
    at tryToString (fs.js:456:3)
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:443:12)


$ sloc ./*.R -a R=r

---------- Result ------------
...

[flosse]

Tanks for reporting this error.
Feel free to fix it, because #99