Inline timesWithWords.

It's a bit unfortunate that we're duplicating code from Sinon itself, but the only other way I can think to make this work is by adding a hard dependency on Sinon (e.g. `require("sinon")`), which is annoying given our UMD wrapper.

lib/sinon-chai.js

@@ -26,6 +26,13 @@
                typeof putativeSpy.calledWithExactly === "function";
     }
 
+    function timesInWords(count) {
+        return count === 1 ? "once" :
+               count === 2 ? "twice" :
+               count === 3 ? "thrice" :
+               (count || 0) + " times";
+    }
+
     function isCall(putativeCall) {
         return putativeCall && isSpy(putativeCall.proxy);
     }
@@ -66,7 +73,7 @@
         utils.addMethod(chai.Assertion.prototype, name, function (arg) {
             assertCanWorkWith(this);
 
-            var messages = getMessages(this._obj, action, nonNegatedSuffix, false, [sinon.timesInWords(arg)]);
+            var messages = getMessages(this._obj, action, nonNegatedSuffix, false, [timesInWords(arg)]);
             this.assert(this._obj[name] === arg, messages.affirmative, messages.negative);
         });
     }