Fix some rubocop issues

Author: mpchadwick

.rubocop.yml

@@ -0,0 +1,6 @@
+AllCops:
+  Exclude:
+    - spec/**/*
+    - jekyll-pre-commit.gemspec
+    - Gemfile
+    - Rakefile

lib/jekyll-pre-commit/checks/check.rb

@@ -1,9 +1,11 @@
 module Jekyll
   module PreCommit
     module Checks
+      # The baseline check class
+      # All checks should extend this class
       class Check
         def initialize
-          @result = { :ok => true, :message => "" }
+          @result = { ok: true, message: '' }
         end
       end
     end