gopls: update x/tools version

Change-Id: Ibf3c3381a3ecb3015b44436b7e28b615fab00bf4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/193378
Run-TryBot: Rebecca Stambler <[email protected]>
Reviewed-by: Ian Cottrell <[email protected]>

Author: stamblerre

gopls/go.mod

@@ -2,6 +2,6 @@ module golang.org/x/tools/gopls
 
 go 1.11
 
-require golang.org/x/tools v0.0.0-20190723021737-8bb11ff117ca
+require golang.org/x/tools v0.0.0-20190904201204-7dc6b39912d7
 
 replace golang.org/x/tools => ../