Use headless chrome for karma specs instead of PhantomJS

PhantomJS is no longer being maintained

config/ng-test.conf.js

@@ -43,7 +43,7 @@ module.exports = function(config) {
 
     autoWatch: true,
 
-    browsers: ['PhantomJS'],
+    browsers: ['ChromeHeadless'],
 
     junitReporter: {
       outputFile: 'log/testacular-unit.xml',

package.json

@@ -6,11 +6,10 @@
     "url": "https://github.com/openfoodfoundation/openfoodnetwork"
   },
   "devDependencies": {
-    "phantomjs-prebuilt": "~2.1.7",
     "karma": "~0.13.22",
+    "karma-chrome-launcher": "~2.2.0",
     "karma-jasmine": "~0.3.8",
     "jasmine-core": "~2.4.1",
-    "karma-phantomjs-launcher": "~1.0.0",
     "karma-coffee-preprocessor": "~0.3.0"
   },
   "license": "AGPL-1.0"