[Refactor] Harden against pathological function names

Change the regular expression for matching the function
name to avoid potential quadratic runtime of the
implementation of `Function.prototype.name` due to the
regular expression in `es6-sham.js:157`.

I'm not aware of any input that would trigger such
behavior, however the fix in this case is trivial. In
fact, both the leading `\s` and trailing `\s` in the
regular expression are unnecessary (though, based on
context, I would say the leading `\s` is actually
necessary, however it currently isn't so...).

Author: ericcornelissen

es6-sham.js

@@ -154,7 +154,7 @@
           return '';
         }
         var str = _call(functionToString, this);
-        var match = _call(_strMatch, str, /\s*function\s+([^(\s]*)\s*/);
+        var match = _call(_strMatch, str, /\s?function\s+([^(\s]*)\s*/);
         var name = match && match[1];
         Object.defineProperty(this, 'name', {
           configurable: true,