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/codegen/interface.go

@@ -0,0 +1,63 @@
+package codegen
+
+import (
+	"go/types"
+
+	"github.com/vektah/gqlparser/ast"
+)
+
+type Interface struct {
+	*ast.Definition
+	Type         types.Type
+	Implementors []InterfaceImplementor
+	InTypemap    bool
+}
+
+type InterfaceImplementor struct {
+	*ast.Definition
+
+	Interface *Interface
+	Type      types.Type
+}
+
+func (b *builder) buildInterface(typ *ast.Definition) *Interface {
+	obj, err := b.Binder.DefaultUserObject(typ.Name)
+	if err != nil {
+		panic(err)
+	}
+
+	i := &Interface{
+		Definition: typ,
+		Type:       obj,
+		InTypemap:  b.Config.Models.UserDefined(typ.Name),
+	}
+
+	for _, implementor := range b.Schema.GetPossibleTypes(typ) {
+		obj, err := b.Binder.DefaultUserObject(implementor.Name)
+		if err != nil {
+			panic(err)
+		}
+
+		i.Implementors = append(i.Implementors, InterfaceImplementor{
+			Definition: implementor,
+			Type:       obj,
+			Interface:  i,
+		})
+	}
+
+	return i
+}
+
+func (i *InterfaceImplementor) ValueReceiver() bool {
+	interfaceType, err := findGoInterface(i.Interface.Type)
+	if interfaceType == nil || err != nil {
+		return true
+	}
+
+	implementorType, err := findGoNamedType(i.Type)
+	if implementorType == nil || err != nil {
+		return true
+	}
+
+	return types.Implements(implementorType, interfaceType)
+}