Add GitLab to Third-Party integration section.

Author: Jason Croft

README.md

@@ -121,9 +121,9 @@ Third-party integration api key settings
 ---
 | service | file path | description |
 | ------- | --------- | ----------- |
-| facebook, twitter, github, dropbox | `config.json` | for signin |
+| facebook, twitter, github, gitlab, dropbox | `config.json` | for signin |
 | imgur | `config.json` | for image upload |
-| google drive, dropbox | `public/js/common.js` | for export and import |
+| gitlab, google drive, dropbox | `public/js/common.js` | for export and import |
 
 DB migration
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