Bump dependencies to be Ruby 2.4+ compatible

Gemfile.lock

@@ -1,15 +1,15 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.5.0)
-      public_suffix (~> 2.0, >= 2.0.2)
+    addressable (2.5.2)
+      public_suffix (>= 2.0.2, < 4.0)
     albino (1.3.3)
       posix-spawn (>= 0.3.6)
     colorator (1.1.0)
-    ffi (1.9.17)
+    ffi (1.9.18)
     forwardable-extended (2.6.0)
-    iconv (1.0.3)
-    jekyll (3.4.0)
+    iconv (1.0.5)
+    jekyll (3.4.5)
       addressable (~> 2.4)
       colorator (~> 1.0)
       jekyll-sass-converter (~> 1.0)
@@ -20,32 +20,37 @@ GEM
       pathutil (~> 0.9)
       rouge (~> 1.7)
       safe_yaml (~> 1.0)
-    jekyll-sass-converter (1.5.0)
+    jekyll-sass-converter (1.5.1)
       sass (~> 3.4)
-    jekyll-watch (1.5.0)
-      listen (~> 3.0, < 3.1)
-    kramdown (1.13.2)
+    jekyll-watch (1.5.1)
+      listen (~> 3.0)
+    kramdown (1.16.2)
     liquid (3.0.6)
-    listen (3.0.8)
+    listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+      ruby_dep (~> 1.2)
     mercenary (0.3.6)
-    pathutil (0.14.0)
+    multi_json (1.13.1)
+    pathutil (0.16.1)
       forwardable-extended (~> 2.6)
-    posix-spawn (0.3.6)
-    public_suffix (2.0.5)
-    pygments.rb (0.6.0)
-      posix-spawn (~> 0.3.6)
-      yajl-ruby (~> 1.1.0)
-    rake (12.0.0)
-    rb-fsevent (0.9.8)
-    rb-inotify (0.9.8)
-      ffi (>= 0.5.0)
-    redcarpet (3.2.2)
+    posix-spawn (0.3.13)
+    public_suffix (3.0.1)
+    pygments.rb (1.2.1)
+      multi_json (>= 1.0.0)
+    rake (12.3.0)
+    rb-fsevent (0.10.2)
+    rb-inotify (0.9.10)
+      ffi (>= 0.5.0, < 2)
+    redcarpet (3.4.0)
     rouge (1.11.1)
+    ruby_dep (1.5.0)
     safe_yaml (1.0.4)
-    sass (3.4.23)
-    yajl-ruby (1.1.0)
+    sass (3.5.5)
+      sass-listen (~> 4.0.0)
+    sass-listen (4.0.0)
+      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-inotify (~> 0.9, >= 0.9.7)
 
 PLATFORMS
   ruby
@@ -59,4 +64,4 @@ DEPENDENCIES
   redcarpet
 
 BUNDLED WITH
-   1.14.3
+   1.16.1