Update nokogiri dependency

Author: githubteacher

Gemfile.lock

@@ -174,7 +174,7 @@ GEM
     minitest (5.10.3)
     multipart-post (2.0.0)
     net-dns (0.8.0)
-    nokogiri (1.8.1)
+    nokogiri (1.8.2)
       mini_portile2 (~> 2.3.0)
     octokit (4.7.0)
       sawyer (~> 0.8.0, >= 0.5.3)