Update pg requirement from = 1.2.1 to = 1.2.2

Updates the requirements on [pg](https://github.com/ged/ruby-pg) to permit the latest version.
- [Release notes](https://github.com/ged/ruby-pg/releases)
- [Changelog](https://github.com/ged/ruby-pg/blob/master/History.rdoc)
- [Commits](ged/ruby-pg@v1.2.1...v1.2.2)

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

Author: dependabot-preview[bot]

sensu-plugins-postgres.gemspec

@@ -39,7 +39,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'sensu-plugin', '~> 4.0'
 
   s.add_runtime_dependency 'dentaku',      '3.3.4'
-  s.add_runtime_dependency 'pg',           '1.2.1'
+  s.add_runtime_dependency 'pg',           '1.2.2'
 
   s.add_development_dependency 'bundler',                   '~> 2.1'
   s.add_development_dependency 'codeclimate-test-reporter', '~> 1.0'