Upgrade Liquid to 3

It has nice new filters such as `default`, `strip`, `uniq`, etc.

Gemfile

@@ -75,7 +75,7 @@ gem 'json', '~> 1.8.1'
 gem 'jsonpath', '~> 0.5.6'
 gem 'kaminari', '~> 0.16.1'
 gem 'kramdown', '~> 1.3.3'
-gem 'liquid', '~> 2.6.1'
+gem 'liquid', '~> 3.0.3'
 gem 'mini_magick'
 gem 'mysql2', '~> 0.3.16'
 gem 'multi_xml'

Gemfile.lock

@@ -235,7 +235,7 @@ GEM
     launchy (2.4.2)
       addressable (~> 2.3)
     libv8 (3.16.14.7)
-    liquid (2.6.2)
+    liquid (3.0.3)
     listen (2.7.9)
       celluloid (>= 0.15.2)
       rb-fsevent (>= 0.9.3)
@@ -529,7 +529,7 @@ DEPENDENCIES
   jsonpath (~> 0.5.6)
   kaminari (~> 0.16.1)
   kramdown (~> 1.3.3)
-  liquid (~> 2.6.1)
+  liquid (~> 3.0.3)
   mini_magick
   mqtt
   multi_xml
@@ -580,3 +580,6 @@ DEPENDENCIES
   weibo_2!
   wunderground (~> 1.2.0)
   xmpp4r (~> 0.5.6)
+
+BUNDLED WITH
+   1.10.5