[BUGFIX beta] Use RegExp.test() for Ember.computed.match.

After a bit of research I believe that `RegExp.test` is quite a bit faster and
results in clearer code (as it returns a boolean instead of a match array).

Quote from the MDN article on `String.match`:

    If you need to know if a string matches a regular expression regexp, use
    regexp.test(string).

Supporting research:

http://jsperf.com/test-vs-match-regex 
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/test 
ttp://stackoverflow.com/a/10940138/1157494

Resolves #3746.