Fixed Naive Parsing of Content-Type HTTP header

It turns out checking for exactly "application/json" is a bad idea since
some servers/web frameworks include stuff like encoding in the header.
For example: Express.js since 4.16.x now set's the content-type header
to: 'application/json; charset=utf-8'.

To remedy this, we now check for the inclusion of application/json in
the string, but don't attempt to match the exact value

lib/request.js

@@ -15,7 +15,8 @@ module.exports = function(method, endpoint, cb, headers) {
       }),
     }).then(res => {
       status = res.status
-      if(res.headers.get('content-type') == 'application/json') {
+      var contentType = res.headers.get("content-type");
+      if(contentType && contentType.includes("application/json")) {
         return res.json();
       } else {
         return res.text();

package.json

@@ -1,6 +1,6 @@
 {
   "name": "yak-orm",
-  "version": "0.0.17",
+  "version": "0.0.18",
   "description": "Yak is an ORM that maps REST resources to JavaScript models/collections",
   "main": "index.js",
   "scripts": {

test/request_test.js

@@ -23,7 +23,7 @@ describe('Request', function() {
             status: 200,
             headers: {
               get: function() {
-                return 'application/json';
+                return 'application/json; charset=utf-8';
               }
             },
             json: function() {