fix Gemfile.lock nokogiri dependencies

Summary:
I installed the ruby dependencies and ran `bundle update nokogiri`. It depends on a newer version of "mini_portile2" which I missed in 9c2f64e148. Now `bundle install` works again.
Closes https://github.com/facebook/rocksdb/pull/3361

Differential Revision: D6710164

Pulled By: ajkr

fbshipit-source-id: 9a08d6cc6400ef495b715b3d68b04ce3f3367031

docs/Gemfile.lock

@@ -105,13 +105,13 @@ GEM
       rb-fsevent (>= 0.9.3)
       rb-inotify (>= 0.9.7)
     mercenary (0.3.6)
-    mini_portile2 (2.1.0)
+    mini_portile2 (2.3.0)
     minima (2.0.0)
     minitest (5.9.1)
     multipart-post (2.0.0)
     net-dns (0.8.0)
     nokogiri (1.8.1)
-      mini_portile2 (~> 2.1.0)
+      mini_portile2 (~> 2.3.0)
     octokit (4.4.1)
       sawyer (~> 0.7.0, >= 0.5.3)
     pathutil (0.14.0)