sandbox: update to Go 1.4.2, pull tour sources from new location
sandbox: update to Go 1.4.2, pull tour sources from new location

Change-Id: I8b77d4d0733a8aaf3022e7abe8b0c728b2fcaa7d
Reviewed-on: https://go-review.googlesource.com/7171
Reviewed-by: Minux Ma <72d850dbd8858b791995463d8539b5a379577f28@golang.org>

phoorichet/playground,heshed/playground,phoorichet/playground,neollie/playground,neollie/playground,adams-sarah/playground,gophergala2016/playground-plus,golang/playground,golang/playground,phoorichet/playground,adams-sarah/playground,heshed/playground,heshed/playground,golang/playground,neollie/playground,adams-sarah/playground,gophergala2016/playground-plus,gophergala2016/playground-plus