cmd/gomobile: add missing latest tag to gobind

Go install requires a version to be provided after the package name.
gomobile init command is updated to reflect this new requirement

Fixes golang/go#50994

Change-Id: I014bd6815d9620415ceb43dd7e0aea3afac60556
GitHub-Last-Rev: 3a07fa6
GitHub-Pull-Request: #75
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/384414
Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: morningsend

cmd/gomobile/init.go

@@ -78,7 +78,7 @@ func runInit(cmd *command) error {
 	}()
 
 	// Make sure gobind is up to date.
-	if err := goInstall([]string{"golang.org/x/mobile/cmd/gobind"}, nil); err != nil {
+	if err := goInstall([]string{"golang.org/x/mobile/cmd/gobind@latest"}, nil); err != nil {
 		return err
 	}
 

cmd/gomobile/init_test.go

@@ -175,7 +175,7 @@ var initTmpl = template.Must(template.New("output").Parse(`GOMOBILE={{.GOPATH}}/
 rm -r -f "$GOMOBILE"
 mkdir -p $GOMOBILE
 WORK={{.GOPATH}}/pkg/gomobile/work
-go install -x golang.org/x/mobile/cmd/gobind
+go install -x golang.org/x/mobile/cmd/gobind@latest
 cp $OPENAL_PATH/include/AL/al.h $GOMOBILE/include/AL/al.h
 mkdir -p $GOMOBILE/include/AL
 cp $OPENAL_PATH/include/AL/alc.h $GOMOBILE/include/AL/alc.h