typo fix _providerUri => providerUri

README.md

@@ -64,7 +64,7 @@ var oauth3 = OAUTH3.create(window.location); // use window.location to set Clien
 // this is any OAuth3-compatible provider, such as oauth3.org
 // in v1.1.0 we'll add backwards compatibility for facebook.com, google.com, etc
 //
-function onChangeProvider(_providerUri) {
+function onChangeProvider(providerUri) {
   // example https://oauth3.org
   return oauth3.setIdentityProvider(providerUri);
 }