doc/install.html: get rid of explicit version number in docs. So that we don't need to update the file each time a new version is released.
doc/install.html: get rid of explicit version number in docs.
So that we don't need to update the file each time a new version is released.

LGTM=dave, r, adg
R=golang-codereviews, dave, josharian, gobot, adg, r
CC=golang-codereviews
https://codereview.appspot.com/48730043

wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old