Bump fluentd from 1.9.0 to 1.9.1

Bumps [fluentd](https://github.com/fluent/fluentd) from 1.9.0 to 1.9.1.
- [Release notes](https://github.com/fluent/fluentd/releases)
- [Changelog](https://github.com/fluent/fluentd/blob/master/CHANGELOG.md)
- [Commits](fluent/fluentd@v1.9.0...v1.9.1)

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

Gemfile.lock

@@ -3,7 +3,7 @@ GEM
   specs:
     ast (2.4.0)
     concurrent-ruby (1.1.5)
-    cool.io (1.5.4)
+    cool.io (1.6.0)
     coveralls (0.8.23)
       json (>= 1.8, < 3)
       simplecov (~> 0.16.1)
@@ -12,7 +12,7 @@ GEM
       tins (~> 1.6)
     diff-lcs (1.3)
     docile (1.3.1)
-    fluentd (1.9.0)
+    fluentd (1.9.1)
       cool.io (>= 1.4.5, < 2.0.0)
       http_parser.rb (>= 0.5.1, < 0.7.0)
       msgpack (>= 1.3.1, < 2.0.0)
@@ -69,7 +69,7 @@ GEM
       rubocop (>= 0.68.1)
     ruby-progressbar (1.10.1)
     ruby2_keywords (0.0.1)
-    serverengine (2.2.0)
+    serverengine (2.2.1)
       sigdump (~> 0.2.2)
     shotgun (0.9.2)
       rack (>= 1.0)