gopls: update go.mod for v0.1.7
gopls: update go.mod for v0.1.7

Change-Id: I8953ba567b7aecb664a093acd5a91370a6e1fde9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/196280
Reviewed-by: Ian Cottrell <52376736e5e84615ec49f9c1843b8acc178b1d8d@google.com>
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools