test(privateMocks): allow replacing $prop with strings with special RegExp semantics

`baseThey` used to construct the testcase description by replacing `$prop` using a RegExp.
If the replacement string contained `$&` (which has a special meaning with RegExps), the resulting
string was not as expected.x

Author: gkalpak

test/helpers/privateMocks.js

@@ -11,7 +11,7 @@ function baseThey(msg, vals, spec, itFn) {
   var valsIsArray = angular.isArray(vals);
 
   angular.forEach(vals, function(val, key) {
-    var m = msg.replace(/\$prop/g, angular.toJson(valsIsArray ? val : key));
+    var m = msg.split('$prop').join(angular.toJson(valsIsArray ? val : key));
     itFn(m, function() {
       /* jshint -W040 : ignore possible strict violation due to use of this */
       spec.call(this, val);