Merge pull request #751 from MetaMask/ClarifyCallbackRole

Add note about callback param to sync method warning

app/scripts/lib/inpage-provider.js

@@ -84,7 +84,7 @@ MetamaskInpageProvider.prototype.send = function (payload) {
     // throw not-supported Error
     default:
       var link = 'https://github.com/MetaMask/faq/blob/master/DEVELOPERS.md#dizzy-all-async---think-of-metamask-as-a-light-client'
-      var message = `The MetaMask Web3 object does not support synchronous methods like ${payload.method}. See ${link} for details.`
+      var message = `The MetaMask Web3 object does not support synchronous methods like ${payload.method} without a callback parameter. See ${link} for details.`
       throw new Error(message)
 
   }