Bump pg from 1.5.5 to 1.5.6

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](https://github.com/ged/ruby-pg/compare/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>

Gemfile.lock

@@ -434,7 +434,7 @@ GEM
       racc
     percy-capybara (5.0.0)
       capybara (>= 3)
-    pg (1.5.5)
+    pg (1.5.6)
     platform-api (3.6.0)
       heroics (~> 0.1.1)
       moneta (~> 1.0.0)