add dockerfile for ror, fix template issue (#718)

samples/server/petstore/ruby-on-rails/Gemfile

@@ -3,14 +3,8 @@ source 'https://rubygems.org'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
 gem 'rails', '~> 5.0.0'
-{{#isDBSQLite}}
 # Use sqlite as the database for Active Record
 gem 'sqlite3', '~> 1.3'
-{{/isDBSQLite}}
-{{#isDBMySQL}}
-# Use mysql as the database for Active Record
-gem 'mysql2', '>= 0.3.18', '< 0.5'
-{{/isDBMySQL}}
 # Use Puma as the app server
 gem 'puma', '~> 3.0'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder