Bump tzinfo-data from 1.2018.5 to 1.2018.6 (#9016)

Bumps [tzinfo-data](https://github.com/tzinfo/tzinfo-data) from 1.2018.5 to 1.2018.6.
- [Release notes](https://github.com/tzinfo/tzinfo-data/releases)
- [Commits](https://github.com/tzinfo/tzinfo-data/compare/v1.2018.5...v1.2018.6)

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

Gemfile.lock

@@ -616,7 +616,7 @@ GEM
       unf (~> 0.1.0)
     tzinfo (1.2.5)
       thread_safe (~> 0.1)
-    tzinfo-data (1.2018.5)
+    tzinfo-data (1.2018.6)
       tzinfo (>= 1.0.0)
     unf (0.1.4)
       unf_ext