goauth2: use an expiry in the past instead of time.Now() in tests
goauth2: use an expiry in the past instead of time.Now() in tests

The tests used time.Now() as an expired token expiry; time.Now() is not,
however, strictly speaking in the past. On a system with low time
resolution, or minor clock jitter, this will cause occasional test
failures. Use a time that is thoroughly in the past instead.
(I wish that Go had a clock package we could use for mock time.)

I did not add a comment in the code because this strikes me as
unlikely to accidentally regress, so a comment would just add noise.

Fixes issue 22.

R=adg, nightlyone
CC=golang-dev
https://codereview.appspot.com/21660043

Committer: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

avisri/goauth2,desireebisco/goauth2,treetopllc/goauth2,MrDangerous/goauth2,skyeunknown084/goauth2,lvzhihao/goauth2,odeke-em/goauth2,epelc/goauth2,happydpc/goauth2,combucha/goauth2,stanwu/goauth2,djacobow/goauth2,pkieltyka/goauth2,aquarat/goauth2,imrickrick/goauth2,mattga/goauth2,hiteshjoshi/goauth2,badu/goauth2,jeisenberg/goauth2,smagic39/goauth2,udhos/goauth2