Bump sequel from 5.6.0 to 5.7.0

Bumps [sequel](https://github.com/jeremyevans/sequel) from 5.6.0 to 5.7.0.
- [Release notes](https://github.com/jeremyevans/sequel/releases)
- [Changelog](https://github.com/jeremyevans/sequel/blob/master/CHANGELOG)
- [Commits](jeremyevans/sequel@5.6.0...5.7.0)

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

Gemfile.lock

@@ -18,7 +18,7 @@ GEM
     rerun (0.13.0)
       listen (~> 3.0)
     ruby_dep (1.5.0)
-    sequel (5.6.0)
+    sequel (5.7.0)
     sinatra (2.0.1)
       mustermann (~> 1.0)
       rack (~> 2.0)