$ rails -v
Rails 4.2.6
$ruby -v
ruby 2.3.1
1.Gemfile
-source 'https://gems.ruby-china.org'
+source 'https://rubygems.org'
.
.
.
-gem 'pg', '~> 0.15'
+gem 'pg', '~> 0.20.0'
.
.
.
2.$bundle install
3.Done
$ rails -v
Rails 4.2.6
$ruby -v
ruby 2.3.1
1.Gemfile
-source 'https://gems.ruby-china.org'
+source 'https://rubygems.org'
.
.
.
-gem 'pg', '~> 0.15'
+gem 'pg', '~> 0.20.0'
.
.
.
2.$bundle install
3.Done