Bump capistrano-maintenance from 1.0.0 to 1.2.0

Bumps [capistrano-maintenance](https://github.com/capistrano/maintenance) from 1.0.0 to 1.2.0.
- [Release notes](https://github.com/capistrano/maintenance/releases)
- [Changelog](https://github.com/capistrano/maintenance/blob/master/CHANGELOG.md)
- [Commits](capistrano/maintenance@v1.0.0...v1.2.0)

Gemfile.lock

@@ -78,7 +78,7 @@ GEM
     capistrano-bundler (1.1.4)
       capistrano (~> 3.1)
       sshkit (~> 1.2)
-    capistrano-maintenance (1.0.0)
+    capistrano-maintenance (1.2.0)
       capistrano (>= 3.0)
     capistrano-rails (1.1.3)
       capistrano (~> 3.1)