Update top-gh-contribs dependency

refs TryGhost#5503

- updates package.json to using 2.0.2 version of top-gh-conribs
- updates gruntfile, using moment to calculate time period to observe
- new version of top-gh-contribs is not related to top 100 contributors therefore returns more users
- observed timepsan is reverted to 90 days now that top-gh-contribs fetches enough contributors

Gruntfile.js

@@ -799,16 +799,14 @@ var _              = require('lodash'),
         // Builds the github contributors partial template used on the Settings/About page,
         // and downloads the avatar for each of the users.
         // Run by any task that compiles the ember assets or manually via `grunt buildAboutPage`.
-        // Change which version you're working against by setting the "releaseTag" below.
-        //
         // Only builds if the contributors template does not exist.
         // To force a build regardless, supply the --force option.
         //     `grunt buildAboutPage --force`
         grunt.registerTask('buildAboutPage', 'Compile assets for the About Ghost page', function () {
             var done = this.async(),
                 templatePath = 'core/client/app/templates/-contributors.hbs',
                 imagePath = 'core/client/public/assets/img/contributors/',
-                timeSpan = Date.now() - (1000 * 60 * 60 * 24 * 180),
+                timeSpan = moment().subtract(90, 'days').format('YYYY-MM-DD'),
                 oauthKey = process.env.GITHUB_OAUTH_KEY;
 
             if (fs.existsSync(templatePath) && !grunt.option('force')) {
@@ -825,7 +823,7 @@ var _              = require('lodash'),
                     user: 'tryghost',
                     repo: 'ghost',
                     oauthKey: oauthKey,
-                    releaseDate: timeSpan,
+                    sinceDate: timeSpan,
                     count: 18,
                     retry: true
                 })

package.json

@@ -93,6 +93,6 @@
     "sinon": "1.14.1",
     "supertest": "1.0.1",
     "testem": "0.8.3",
-    "top-gh-contribs": "1.0.1"
+    "top-gh-contribs": "2.0.2"
   }
 }