Use vendor when building (#201)

* Use vendor code for all go calls

* Add missing vendor dependencies

* Add travis_retry to yarn install

* Fix go test call

vendor/github.com/99designs/gqlgen/main.go

@@ -0,0 +1,9 @@
+package main
+
+import (
+	"github.com/99designs/gqlgen/cmd"
+)
+
+func main() {
+	cmd.Execute()
+}