Update Gson to 1.7.1
Update Gson to 1.7.1

Change-Id: I02b6284c70b72ae12b3e6f787127d351aeb491b1

GerritCodeReview/gwtjsonrpc,1yvT0s/gerrit.gwtjsonrpc,CandyShop/gerrit.gwtjsonrpc,GerritCodeReview/gwtjsonrpc,evanchueng/gerrit.gwtjsonrpc