Merge pull request #260 from corburn/patch-1

fix error message typo

Author: marco-c

src/web-push-lib.js

@@ -32,7 +32,7 @@ WebPushLib.prototype.setGCMAPIKey = function(apiKey) {
 
   if (typeof apiKey === 'undefined' || typeof apiKey !== 'string' ||
     apiKey.length === 0) {
-    throw new Error('The GCM API Key should be a non-emtpy string or null.');
+    throw new Error('The GCM API Key should be a non-empty string or null.');
   }
 
   gcmAPIKey = apiKey;