Fix non ES5 compliant regexp

ES5 appears to require that { be escaped when not used as part of a quantifier. While this works fine in browsers it appears to choke less lenient runtimes (e.g. Duktape).

Author: zetaben

lib/chai/utils/getMessage.js

@@ -43,9 +43,9 @@ module.exports = function (obj, args) {
   if(typeof msg === "function") msg = msg();
   msg = msg || '';
   msg = msg
-    .replace(/#{this}/g, function () { return objDisplay(val); })
-    .replace(/#{act}/g, function () { return objDisplay(actual); })
-    .replace(/#{exp}/g, function () { return objDisplay(expected); });
+    .replace(/#\{this\}/g, function () { return objDisplay(val); })
+    .replace(/#\{act\}/g, function () { return objDisplay(actual); })
+    .replace(/#\{exp\}/g, function () { return objDisplay(expected); });
 
   return flagMsg ? flagMsg + ': ' + msg : msg;
 };