chore(deps): bump pg from 1.5.5 to 1.5.6 in /pact_broker

Bumps [pg](https://github.com/ged/ruby-pg) from 1.5.5 to 1.5.6.
- [Changelog](https://github.com/ged/ruby-pg/blob/master/History.md)
- [Commits](ged/ruby-pg@v1.5.5...v1.5.6)

---
updated-dependencies:
- dependency-name: pg
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

pact_broker/Gemfile.lock

@@ -101,7 +101,7 @@ GEM
       thor (~> 1.0)
     padrino-support (0.15.3)
     parslet (2.0.0)
-    pg (1.5.5)
+    pg (1.5.6)
     psych (4.0.6)
       stringio
     puma (5.6.8)