Bump pg from 1.5.4 to 1.5.9

Bumps [pg](https://github.com/ged/ruby-pg) from 1.5.4 to 1.5.9.
- [Changelog](https://github.com/ged/ruby-pg/blob/master/History.md)
- [Commits](ged/ruby-pg@v1.5.4...v1.5.9)

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

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

Author: dependabot[bot]

Gemfile.lock

@@ -275,7 +275,7 @@ GEM
     parser (3.3.3.0)
       ast (~> 2.4.1)
       racc
-    pg (1.5.4)
+    pg (1.5.9)
     pickadate-rails (3.5.6.0)
       railties (>= 3.1.0)
     popper_js (2.11.8)