[release-branch.go1.4] go-tour: update sub-repo import paths

««« CL 178510043 / 27216d4d0984
gotour: update sub-repo import paths

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/178510043
»»»

««« CL 176670043 / 87dccf852df4
go-tour: update sub-repo import path
I missed the appengine one in last CL.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/176670043
»»»

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/185790043
3 files changed