fix bug by correcting the separator character (SharePoint#866)

Proposing a change to this guidance document to reflect bug fix pull request to the source code repository. Pull Request: pnp/sp-dev-fx-webparts#312

Author: kngrace

docs/spfx/web-parts/guidance/call-microsoft-graph-from-your-web-part.md

@@ -126,7 +126,7 @@ AuthenticationContext.prototype._renewToken = function (resource, callback) {
   this._renewTokenSuper(resource, callback);
   var _renewStates = this._getItem('renewStates');
   if (_renewStates) {
-    _renewStates = _renewStates.split(';');
+    _renewStates = _renewStates.split(',');
   }
   else {
     _renewStates = [];
@@ -256,4 +256,4 @@ Because client-side applications are incapable of securely storing secrets, and
 
 ## More information
 
-- [Authentication Scenarios for Azure AD](https://Azure.microsoft.com/en-us/documentation/articles/active-directory-authentication-scenarios/)
+- [Authentication Scenarios for Azure AD](https://Azure.microsoft.com/en-us/documentation/articles/active-directory-authentication-scenarios/)