Add missing license header to files

Change-Id: Id7a4afc9825d6e36375f481a5e0868dc30515115

Author: skriptble

x/bsonx/bson_test.go

@@ -1,3 +1,9 @@
+// Copyright (C) MongoDB, Inc. 2017-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
 package bsonx
 
 import (

x/bsonx/mdocument_test.go

@@ -1,3 +1,9 @@
+// Copyright (C) MongoDB, Inc. 2017-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
 package bsonx
 
 import (

x/bsonx/primitive_codecs.go

@@ -1,3 +1,9 @@
+// Copyright (C) MongoDB, Inc. 2017-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
 package bsonx
 
 import (