internal/goversion: update to 1.14

In #33848, we propose to use 'go 1.14' in the go.mod file to enable
new default behavior. That means that 'go mod init' needs to start
generating that directive by default, which requires the presence of
the updated version tag in the build environment.

Updates #33848

Change-Id: I9f3b8845fdfd843fd76de32f4b55d8f765d691de
Reviewed-on: https://go-review.googlesource.com/c/go/+/198318


Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>