Use jekyll-assets for asset compilation

Gemfile.lock

@@ -14,11 +14,15 @@ GEM
       execjs
     coffee-script-source (1.12.2)
     colorator (1.1.0)
+    concurrent-ruby (1.0.5)
     ethon (0.10.1)
       ffi (>= 1.3.0)
     execjs (2.7.0)
+    extras (0.3.0)
+      forwardable-extended (~> 2.5)
     faraday (0.12.1)
       multipart-post (>= 1.2, < 3)
+    fastimage (2.1.0)
     ffi (1.9.18)
     forwardable-extended (2.6.0)
     gemoji (3.0.0)
@@ -85,6 +89,14 @@ GEM
       pathutil (~> 0.9)
       rouge (~> 1.7)
       safe_yaml (~> 1.0)
+    jekyll-assets (2.3.2)
+      concurrent-ruby (~> 1.0)
+      extras (~> 0.2)
+      fastimage (~> 2.0, >= 1.8)
+      jekyll (~> 3.1, >= 3.0)
+      pathutil (>= 0.8)
+      rack (~> 1.6)
+      sprockets (~> 3.3, < 3.8)
     jekyll-avatar (0.4.2)
       jekyll (~> 3.0)
     jekyll-coffeescript (1.0.1)
@@ -177,6 +189,7 @@ GEM
       forwardable-extended (~> 2.6)
     powerpack (0.1.1)
     public_suffix (2.0.5)
+    rack (1.6.8)
     rainbow (2.2.1)
     rake (12.0.0)
     rb-fsevent (0.10.2)
@@ -196,6 +209,9 @@ GEM
     sawyer (0.8.1)
       addressable (>= 2.3.5, < 2.6)
       faraday (~> 0.8, < 1.0)
+    sprockets (3.7.1)
+      concurrent-ruby (~> 1.0)
+      rack (> 1, < 3)
     terminal-table (1.8.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
     thread_safe (0.3.6)
@@ -210,6 +226,7 @@ PLATFORMS
 
 DEPENDENCIES
   github-pages
+  jekyll-assets
   jekyll-pants
   jekyll-seo-tag
   jekyll-sitemap