Fix broken reference to test-fixture repo in package.json
Fix broken reference to test-fixture repo in package.json

marcinkubicki/web-component-tester,hvdb/web-component-tester,Polymer/web-component-tester,Polymer/tools,sankethkatta/web-component-tester,sankethkatta/web-component-tester,Polymer/tools,hvdb/web-component-tester,fearphage/web-component-tester,Polymer/tools,marcinkubicki/web-component-tester,fearphage/web-component-tester,fearphage/web-component-tester,Polymer/tools,sankethkatta/web-component-tester,Polymer/web-component-tester,Polymer/web-component-tester,marcinkubicki/web-component-tester,hvdb/web-component-tester