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.lock

@@ -153,7 +153,6 @@ GEM
       railties (>= 3.2.16)
     json (2.2.0)
     jwt (2.2.1)
-    libv8 (7.3.492.27.1)
     listen (3.0.8)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
@@ -173,8 +172,6 @@ GEM
     mimemagic (0.3.3)
     mini_mime (1.0.2)
     mini_portile2 (2.4.0)
-    mini_racer (0.2.6)
-      libv8 (>= 6.9.411)
     minitest (5.11.3)
     msgpack (1.3.0)
     multi_json (1.13.1)
@@ -326,6 +323,8 @@ GEM
     turbolinks-source (5.2.0)
     tzinfo (1.2.5)
       thread_safe (~> 0.1)
+    tzinfo-data (1.2019.3)
+      tzinfo (>= 1.0.0)
     uglifier (4.1.20)
       execjs (>= 0.3.0, < 3)
     unicode-display_width (1.6.0)
@@ -369,7 +368,6 @@ DEPENDENCIES
   jquery-ui-rails
   listen (~> 3.0.5)
   lograge
-  mini_racer
   net-ldap
   omniauth
   omniauth-bn-launcher!