Update pg requirement from >= 0.18, <= 1.6 to >= 0.18, <= 1.7 (#552)

Updates the requirements on [pg](https://github.com/ged/ruby-pg) to permit the latest version.
- [Changelog](https://github.com/ged/ruby-pg/blob/master/CHANGELOG.md)
- [Commits](ged/ruby-pg@v0.18.0...v1.6.1)

---
updated-dependencies:
- dependency-name: pg
  dependency-version: 1.6.1
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile

@@ -17,7 +17,7 @@ group :development, :test do
   gem "bundler", "~> 2"
   gem "gc_ruboconfig", "~> 5.0.0"
   gem "mysql2", ">= 0.4", "< 0.6"
-  gem "pg", ">= 0.18", "<= 1.6"
+  gem "pg", ">= 0.18", "<= 1.7"
   gem "pry"
   gem "rake", "~> 13.2.1"
   gem "rspec", "~> 3.1"