cmd/gopherbot: fix missing import

I must have not rebased CL 241271 before submitting, because somehow,
there's a missing import.

Change-Id: Id050fb547258a2733935f90f35260a60a3815fb2
Reviewed-on: https://go-review.googlesource.com/c/build/+/241858
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

cmd/gopherbot/gopherbot.go

@@ -33,6 +33,7 @@ import (
 	"golang.org/x/build/devapp/owners"
 	"golang.org/x/build/gerrit"
 	"golang.org/x/build/internal/foreach"
+	"golang.org/x/build/internal/gophers"
 	"golang.org/x/build/internal/secret"
 	"golang.org/x/build/maintner"
 	"golang.org/x/build/maintner/godata"