GRN2-241: Switched Docker base image to Alpine (#853)

* Switched to alpine image

* Switch Docker base image to alpine

* Removed uneeded code

* Slimmed it down even further

Gemfile

@@ -23,7 +23,7 @@ gem 'uglifier', '>= 1.3.0'
 gem 'coffee-rails', '~> 4.2'
 
 # See https://github.com/rails/execjs#readme for more supported runtimes
-gem 'mini_racer', platforms: :ruby
+# gem 'mini_racer', platforms: :ruby
 
 # Use jquery as the JavaScript library
 gem 'jquery-rails', '~> 4.3.3'
@@ -121,7 +121,7 @@ end
 gem 'remote_syslog_logger'
 
 # Windows does not include zoneinfo files, so bundle the tzinfo-data gem
-gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
+gem 'tzinfo-data'
 
 gem 'coveralls', require: false