Use HTTPS to fetch activeadmin gem from GitHub

- This prevents the error which says using 'git://' is not secure.
 - Use HTTPS link instead to fetch the gem

Gemfile.lock

@@ -1,8 +1,8 @@
 GIT
-  remote: git://github.com/activeadmin/activeadmin.git
-  revision: a3fca244b0cbaa6139931952ba2c72dda58e05b1
+  remote: https://github.com/activeadmin/activeadmin.git
+  revision: b1f96a39c6126364c661a952be28000e39d73938
   specs:
-    activeadmin (1.0.0.pre2)
+    activeadmin (1.0.0.pre4)
       arbre (~> 1.0, >= 1.0.2)
       bourbon
       coffee-rails
@@ -11,10 +11,11 @@ GIT
       inherited_resources (~> 1.6)
       jquery-rails
       jquery-ui-rails
-      kaminari (~> 0.15)
-      rails (>= 3.2, < 5.0)
+      kaminari (>= 0.15, < 2.0)
+      railties (>= 3.2, < 5.1)
       ransack (~> 1.3)
       sass-rails
+      sprockets (< 4.1)
 
 GEM
   remote: https://rubygems.org/
@@ -54,13 +55,13 @@ GEM
       minitest (~> 5.1)
       thread_safe (~> 0.3, >= 0.3.4)
       tzinfo (~> 1.1)
-    arbre (1.0.3)
+    arbre (1.1.1)
       activesupport (>= 3.0.0)
     arel (6.0.3)
     bcrypt (3.1.10)
     binding_of_caller (0.7.2)
       debug_inspector (>= 0.0.1)
-    bourbon (4.2.5)
+    bourbon (4.2.7)
       sass (~> 3.4)
       thor (~> 0.19)
     builder (3.2.2)
@@ -91,9 +92,9 @@ GEM
     factory_girl_rails (4.5.0)
       factory_girl (~> 4.5.0)
       railties (>= 3.0.0)
-    formtastic (3.1.3)
+    formtastic (3.1.4)
       actionpack (>= 3.2.13)
-    formtastic_i18n (0.4.1)
+    formtastic_i18n (0.6.0)
     gcm (0.1.0)
       httparty
       json
@@ -118,12 +119,21 @@ GEM
       rails-dom-testing (~> 1.0)
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
-    jquery-ui-rails (5.0.5)
+    jquery-ui-rails (6.0.1)
       railties (>= 3.2.16)
     json (1.8.3)
-    kaminari (0.16.3)
-      actionpack (>= 3.0.0)
-      activesupport (>= 3.0.0)
+    kaminari (1.0.0)
+      activesupport (>= 4.1.0)
+      kaminari-actionview (= 1.0.0)
+      kaminari-activerecord (= 1.0.0)
+      kaminari-core (= 1.0.0)
+    kaminari-actionview (1.0.0)
+      actionview
+      kaminari-core (= 1.0.0)
+    kaminari-activerecord (1.0.0)
+      activerecord
+      kaminari-core (= 1.0.0)
+    kaminari-core (1.0.0)
     libv8 (3.16.14.11)
     loofah (2.0.3)
       nokogiri (>= 1.5.9)
@@ -139,7 +149,7 @@ GEM
       mini_portile (~> 0.6.0)
     orm_adapter (0.5.0)
     pg (0.18.2)
-    polyamorous (1.2.0)
+    polyamorous (1.3.1)
       activerecord (>= 3.0)
     rack (1.6.4)
     rack-test (0.6.3)
@@ -169,12 +179,12 @@ GEM
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
     rake (10.4.2)
-    ransack (1.7.0)
+    ransack (1.8.2)
       actionpack (>= 3.0)
       activerecord (>= 3.0)
       activesupport (>= 3.0)
       i18n
-      polyamorous (~> 1.2)
+      polyamorous (~> 1.3)
     rdoc (4.2.0)
       json (~> 1.4)
     ref (2.0.0)
@@ -271,6 +281,3 @@ DEPENDENCIES
   turbolinks
   uglifier (>= 1.3.0)
   web-console (~> 2.0)
-
-BUNDLED WITH
-   1.13.7