[MM-17889] Implement validation of plugin API version comments (#11941)

go.mod

@@ -88,6 +88,7 @@ require (
 	golang.org/x/net v0.0.0-20190628185345-da137c7871d7
 	golang.org/x/sys v0.0.0-20190712062909-fae7ac547cb7 // indirect
 	golang.org/x/text v0.3.2
+	golang.org/x/tools v0.0.0-20190606124116-d0a3d012864b
 	google.golang.org/appengine v1.6.1 // indirect
 	google.golang.org/genproto v0.0.0-20190716160619-c506a9f90610 // indirect
 	google.golang.org/grpc v1.22.0 // indirect