Bump pg gem from 1.1.3 to 1.1.4

This keeps the version used by gitlab-monitor and GitLab CE
consistent. This release also adds Ruby 2.6 support and PostgreSQL 11
error codes:

https://github.com/ged/ruby-pg/blob/master/History.rdoc

Gemfile.lock

@@ -583,7 +583,7 @@ GEM
       atomic (>= 1.0.0)
       peek
       redis
-    pg (1.1.3)
+    pg (1.1.4)
     po_to_json (1.0.1)
       json (>= 1.6.0)
     powerpack (0.1.1)