Bump pghero from 2.3.0 to 2.4.0

Bumps [pghero](https://github.com/ankane/pghero) from 2.3.0 to 2.4.0.
- [Release notes](https://github.com/ankane/pghero/releases)
- [Changelog](https://github.com/ankane/pghero/blob/master/CHANGELOG.md)
- [Commits](ankane/pghero@v2.3.0...v2.4.0)

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

Gemfile.lock

@@ -161,7 +161,7 @@ GEM
     mime-types-data (3.2019.0904)
     mini_mime (1.0.2)
     mini_portile2 (2.4.0)
-    minitest (5.12.2)
+    minitest (5.13.0)
     multi_xml (0.6.0)
     multipart-post (2.1.1)
     nenv (0.3.0)
@@ -181,7 +181,7 @@ GEM
     path_expander (1.1.0)
     pg (1.1.4)
     pg_query (1.1.0)
-    pghero (2.3.0)
+    pghero (2.4.0)
       activerecord (>= 5)
     pronto (0.10.0)
       gitlab (~> 4.0, >= 4.0.0)