Bump nokogiri from 1.6.8.1 to 1.9.1

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.6.8.1 to 1.9.1.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.6.8.1...v1.9.1)

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -37,30 +37,29 @@ GEM
       thread_safe (~> 0.3, >= 0.3.4)
       tzinfo (~> 1.1)
     arel (6.0.3)
-    builder (3.2.2)
+    builder (3.2.3)
     concurrent-ruby (1.1.5)
     crass (1.0.5)
     erubis (2.7.0)
-    globalid (0.3.6)
-      activesupport (>= 4.1.0)
-    i18n (0.7.0)
+    globalid (0.4.2)
+      activesupport (>= 4.2.0)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
     jquery-rails (3.1.4)
       railties (>= 3.0, < 5.0)
       thor (>= 0.14, < 2.0)
-    json (1.8.3)
+    json (1.8.6)
     kgio (2.9.2)
     loofah (2.3.1)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)
-    mail (2.6.4)
-      mime-types (>= 1.16, < 4)
-    mime-types (3.1)
-      mime-types-data (~> 3.2015)
-    mime-types-data (3.2016.0521)
-    mini_portile2 (2.1.0)
-    minitest (5.9.0)
-    nokogiri (1.6.8.1)
-      mini_portile2 (~> 2.1.0)
+    mail (2.7.1)
+      mini_mime (>= 0.1.1)
+    mini_mime (1.0.2)
+    mini_portile2 (2.4.0)
+    minitest (5.13.0)
+    nokogiri (1.9.1)
+      mini_portile2 (~> 2.4.0)
     pg (0.17.1)
     rack (1.6.11)
     rack-cors (0.2.9)
@@ -79,9 +78,9 @@ GEM
       sprockets-rails
     rails-deprecated_sanitizer (1.0.3)
       activesupport (>= 4.2.0.alpha)
-    rails-dom-testing (1.0.7)
-      activesupport (>= 4.2.0.beta, < 5.0)
-      nokogiri (~> 1.6.0)
+    rails-dom-testing (1.0.9)
+      activesupport (>= 4.2.0, < 5.0)
+      nokogiri (~> 1.6)
       rails-deprecated_sanitizer (>= 1.0.1)
     rails-html-sanitizer (1.3.0)
       loofah (~> 2.3)
@@ -109,8 +108,8 @@ GEM
       activesupport (>= 4.0)
       sprockets (>= 3.0.0)
     thor (0.19.1)
-    thread_safe (0.3.5)
-    tzinfo (1.2.2)
+    thread_safe (0.3.6)
+    tzinfo (1.2.5)
       thread_safe (~> 0.1)
     unicorn (4.8.2)
       kgio (~> 2.6)