As noticed by @riking, the logic in the bash script will break
when Go 1 version numbers reach double-digits.
Instead, use a build tag "!go1.5" to cause a syntax error:
$ /opt/go1.4.3/bin/go build
can't load package: package github.com/rfjakob/gocryptfs:
go1.4.go:5:1: expected 'package', found 'STRING' "You need Go 1.5 or higher to compile gocryptfs!"
Fixes https://github.com/rfjakob/gocryptfs/issues/133
Jakob Unterwurzacher