Upgrade html-proofer and dependencies to latest

Upgraded via:
  rbenv exec bundle update html-proofer

Author: swegner

website/Gemfile.lock

@@ -1,7 +1,7 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (4.2.10)
+    activesupport (4.2.11)
       i18n (~> 0.7)
       minitest (~> 5.1)
       thread_safe (~> 0.3, >= 0.3.4)
@@ -10,12 +10,12 @@ GEM
       public_suffix (>= 2.0.2, < 4.0)
     colorator (1.1.0)
     colorize (0.8.1)
-    concurrent-ruby (1.0.5)
+    concurrent-ruby (1.1.4)
     ethon (0.11.0)
       ffi (>= 1.3.0)
-    ffi (1.9.21)
+    ffi (1.9.25)
     forwardable-extended (2.6.0)
-    html-proofer (3.8.0)
+    html-proofer (3.9.3)
       activesupport (>= 4.2, < 6.0)
       addressable (~> 2.3)
       colorize (~> 0.8)
@@ -54,12 +54,12 @@ GEM
     mercenary (0.3.6)
     mini_portile2 (2.3.0)
     minitest (5.11.3)
-    nokogiri (1.8.2)
+    nokogiri (1.8.5)
       mini_portile2 (~> 2.3.0)
     parallel (1.12.1)
     pathutil (0.16.1)
       forwardable-extended (~> 2.6)
-    public_suffix (3.0.2)
+    public_suffix (3.0.3)
     rake (12.3.0)
     rb-fsevent (0.10.2)
     rb-inotify (0.9.10)
@@ -73,7 +73,7 @@ GEM
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
     thread_safe (0.3.6)
-    typhoeus (1.3.0)
+    typhoeus (1.3.1)
       ethon (>= 0.9.0)
     tzinfo (1.2.5)
       thread_safe (~> 0.1)
@@ -92,4 +92,4 @@ DEPENDENCIES
   rake
 
 BUNDLED WITH
-   1.16.0
+   1.16.2