Fix packr2 install by using go install at a version

Signed-off-by: Luis Pabón <[email protected]>

Makefile

@@ -108,7 +108,7 @@ $(GOPATH)/bin/errcheck:
 
 $(GOPATH)/bin/packr2:
  @echo "Installing missing $@ ..."
- GO111MODULE=off go get -u github.com/gobuffalo/packr/...
+ go install github.com/gobuffalo/packr/v2/[email protected]
 
 $(GOPATH)/bin/cover:
  @echo "Installing missing $@ ..."