docs: Fixed error in code sample.

The code sample for GooglePlayServicesUtil.getErrorDialog had an
error, per bug report from the community. Staged the fixed doc to

http://asolovay.mtv:9860/training/location/retrieve-current.html#CheckServices

Aron, it looks like you've edited GooglePlayServicesUtil.java so I
hoped you could give it a +1. If not you, can you suggest someone?

bug: 17009860
Change-Id: Id5cbf13d2b771cfe168f1b4cb1abd5e339f1ac60