chore(package): update gh-pages to version 2.1.1

Closes #41

Author: greenkeeper[bot]

package.json

@@ -18,7 +18,7 @@
     "@vuepress/plugin-medium-zoom": "^1.0.0-alpha.23",
     "@vuepress/plugin-notification": "^1.0.0-alpha.23",
     "@vuepress/plugin-pwa": "^1.0.0-alpha.23",
-    "gh-pages": "^1.0.0",
+    "gh-pages": "^2.1.1",
     "timeago.js": "^4.0.0-beta.1",
     "vuepress": "^1.0.0-alpha.23",
     "vuepress-plugin-flowchart": "^1.4.2"