Fixed the issue #166 related to parsing of extend type declaration

Author: nemanja-stanarevic

src/language/__tests__/schema-kitchen-sink.graphql

@@ -32,3 +32,7 @@ input InputType {
   key: String!
   answer: Int = 42
 }
+
+extend type Foo {
+  seven(argument: [String]): Type
+}

src/language/__tests__/schema-printer.js

@@ -77,6 +77,10 @@ input InputType {
   key: String!
   answer: Int = 42
 }
+
+extend type Foo {
+  seven(argument: [String]): Type
+}
 `);
 
   });

src/language/parser.js

@@ -92,7 +92,7 @@ import {
   ENUM_VALUE_DEFINITION,
   INPUT_OBJECT_TYPE_DEFINITION,
 
-  TYPE_EXTENTION_DEFINITION,
+  TYPE_EXTENSION_DEFINITION,
 } from './kinds';
 
 
@@ -893,7 +893,7 @@ function parseTypeExtensionDefinition(parser): TypeExtensionDefinition {
   expectKeyword(parser, 'extend');
   var definition = parseObjectTypeDefinition(parser);
   return {
-    kind: TYPE_EXTENTION_DEFINITION,
+    kind: TYPE_EXTENSION_DEFINITION,
     definition,
     loc: loc(parser, start),
   };