use postgresql for production

Gemfile

@@ -3,8 +3,7 @@ source 'https://rubygems.org'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '5.1.1'
-# Use sqlite3 as the database for Active Record
-gem 'sqlite3'
+
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
@@ -64,6 +63,8 @@ end
 group :local, :development, :test do
   gem 'factory_girl_rails'
   gem 'faker'
+  # Use sqlite3 as the database for Active Record
+  gem 'sqlite3'
 end
 
 # NOTE: install mailcatcher for development
@@ -79,3 +80,8 @@ end
 group :test do
   gem 'simplecov', :require => false
 end
+
+group :production do
+  # Use postgresql as the database for Active Record
+  gem 'pg'
+end