go.tools: fix various typos
go.tools: fix various typos

LGTM=adonovan
R=adonovan
CC=golang-codereviews
https://golang.org/cl/97920045

evandbrown/build,proppy/build,golang/build,proppy/build,proppy/build,evandbrown/build,evandbrown/build,proppy/build,golang/build,golang/build,golang/build