Bump oauth from 0.4.7 to 0.5.6

Bumps [oauth](https://github.com/oauth-xx/oauth-ruby) from 0.4.7 to 0.5.6.
- [Release notes](https://github.com/oauth-xx/oauth-ruby/releases)
- [Changelog](https://github.com/oauth-xx/oauth-ruby/blob/master/HISTORY)
- [Commits](https://github.com/oauth-xx/oauth-ruby/compare/v0.4.7...v0.5.6)

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -211,7 +211,7 @@ GEM
     nokogiri (1.6.3.1)
       mini_portile (= 0.6.0)
     non-stupid-digest-assets (1.0.4)
-    oauth (0.4.7)
+    oauth (0.5.6)
     orm_adapter (0.5.0)
     polyamorous (1.1.0)
       activerecord (>= 3.0)