Fix ReferenceErrors since we can't qualify with window

btw, this is the worst language. Fixes #287

Author: mattrobenolt

src/raven.js

@@ -4,7 +4,7 @@
 // If there is no JSON, we no-op the core features of Raven
 // since JSON is required to encode the payload
 var _Raven = window.Raven,
-    hasJSON = !!(isObject(JSON) && JSON.stringify),
+    hasJSON = !!(typeof JSON === 'object' && JSON.stringify),
     lastCapturedException,
     lastEventId,
     globalServer,

template/_footer.js

@@ -4,10 +4,10 @@ if (typeof define === 'function' && define.amd) {
     define('raven', function(Raven) {
       return (window.Raven = Raven);
     });
-} else if (isObject(module)) {
+} else if (typeof module === 'object') {
     // browserify
     module.exports = Raven;
-} else if (isObject(exports)) {
+} else if (typeof exports === 'object') {
     // CommonJS
     exports = Raven;
 } else {