Bump octokit from 4.14.0 to 4.15.0

Bumps [octokit](https://github.com/octokit/octokit.rb) from 4.14.0 to 4.15.0.
- [Release notes](https://github.com/octokit/octokit.rb/releases)
- [Changelog](https://github.com/octokit/octokit.rb/blob/4-stable/RELEASE.md)
- [Commits](octokit/octokit.rb@v4.14.0...v4.15.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -27,7 +27,7 @@ GEM
     docile (1.3.2)
     emot (0.0.4)
       thor
-    faraday (0.17.1)
+    faraday (0.17.3)
       multipart-post (>= 1.2, < 3)
     fastimage (2.1.7)
     hikidoc (0.1.0)
@@ -51,7 +51,8 @@ GEM
     multipart-post (2.1.1)
     nokogiri (1.10.7)
       mini_portile2 (~> 2.4.0)
-    octokit (4.14.0)
+    octokit (4.15.0)
+      faraday (>= 0.9)
       sawyer (~> 0.8.0, >= 0.5.3)
     phantomjs (2.1.1.0)
     pit (0.0.7)
@@ -62,7 +63,7 @@ GEM
     pry-byebug (3.7.0)
       byebug (~> 11.0)
       pry (~> 0.10)
-    public_suffix (4.0.1)
+    public_suffix (3.1.1)
     rack (2.0.8)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)