Merge pull request #17 from slack-ruby/dependabot/bundler/rack-2.0.8

Bump rack from 2.0.7 to 2.0.8

Author: dblock

Gemfile.lock

@@ -154,7 +154,7 @@ GEM
     parser (2.6.5.0)
       ast (~> 2.4.0)
     public_suffix (4.0.1)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-accept (0.4.5)
       rack (>= 0.4)
     rack-cors (1.0.6)