Remove deprecated code.google.com imports

[Emile Vauge]

Hi,

As code.google.com is shutting down, I get a warning when using ghr:
warning: code.google.com is shutting down; import path code.google.com/p/goauth2/oauth will stop working.
Could you use golang.org/x/oauth2 instead of code.google.com/p/goauth2/oauth here

ghr/client.go

Line 8 in 351713c

 "code.google.com/p/goauth2/oauth" 

?

[Taichi Nakashima]

OK. Thank you for reporting