support postgres in production

Gemfile

@@ -11,6 +11,9 @@ gem 'rails', '~> 5.0.7'
 # Use Puma as the app server
 gem 'puma', '~> 3.0'
 
+# Use SQLite as the primary database.
+gem 'sqlite3'
+
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 
@@ -62,9 +65,6 @@ group :production do
 end
 
 group :development, :test do
-  # Use SQLite in development and test.
-  gem 'sqlite3'
-
   # Call 'byebug' anywhere in the code to stop execution and get a debugger console
   gem 'byebug', platform: :mri