Revert "Use jekyll-assets"

This reverts commit 9062937951.

Gemfile.lock

@@ -14,14 +14,11 @@ GEM
       execjs
     coffee-script-source (1.10.0)
     colorator (0.1)
-    concurrent-ruby (1.0.1)
     ethon (0.8.1)
       ffi (>= 1.3.0)
     execjs (2.6.0)
     faraday (0.9.2)
       multipart-post (>= 1.2, < 3)
-    fastimage (1.8.1)
-      addressable (~> 2.3, >= 2.3.5)
     ffi (1.9.10)
     gemoji (2.1.0)
     github-pages (64)
@@ -66,12 +63,6 @@ GEM
       mercenary (~> 0.3.3)
       rouge (~> 1.7)
       safe_yaml (~> 1.0)
-    jekyll-assets (2.1.2)
-      fastimage (~> 1.8)
-      jekyll (~> 3.0)
-      sprockets (~> 3.3)
-      sprockets-helpers (~> 1.2)
-      tilt (~> 2.0)
     jekyll-coffeescript (1.0.1)
       coffee-script (~> 2.2)
     jekyll-feed (0.4.0)
@@ -114,7 +105,6 @@ GEM
     octokit (4.3.0)
       sawyer (~> 0.7.0, >= 0.5.3)
     public_suffix (1.5.3)
-    rack (1.6.4)
     rb-fsevent (0.9.7)
     rb-inotify (0.9.7)
       ffi (>= 0.5.0)
@@ -126,14 +116,8 @@ GEM
     sawyer (0.7.0)
       addressable (>= 2.3.5, < 2.5)
       faraday (~> 0.8, < 0.10)
-    sprockets (3.5.2)
-      concurrent-ruby (~> 1.0)
-      rack (> 1, < 3)
-    sprockets-helpers (1.2.1)
-      sprockets (>= 2.2)
     terminal-table (1.5.2)
     thread_safe (0.3.5)
-    tilt (2.0.2)
     typhoeus (0.8.0)
       ethon (>= 0.8.0)
     tzinfo (1.2.2)
@@ -144,7 +128,6 @@ PLATFORMS
 
 DEPENDENCIES
   github-pages
-  jekyll-assets
 
 BUNDLED WITH
    1.11.2