gimme: Add arm64 version warning
gimme: Add arm64 version warning

arm64 support was added in go1.5.  Print an error messsage and fail
if an older version is requested.

Signed-off-by: lupan2005 <b59ab7d3e845a6c3d0768c2976a0cbc25494522f@gmail.com>
[Split off from larger patch and cleaned up.]
Signed-off-by: Geoff Levand <c3918f39022407dee6a0056ceca9b1aa80e8e4ce@infradead.org>

glevand/travis-ci--gimme,kofalt/gimme,meatballhat/gimme,glevand/travis-ci--gimme,travis-ci/gimme,travis-ci/gimme