Change coverage output format to json

Author: Umekawa

spec/spec_helper.rb

@@ -1,6 +1,13 @@
 if ENV["CI"]
   require "simplecov"
-  SimpleCov.start
+  require "simplecov_json_formatter"
+  SimpleCov.start do
+    formatter SimpleCov::Formatter::MultiFormatter.new([
+                                                         SimpleCov::Formatter::JSONFormatter,
+                                                         SimpleCov::Formatter::HTMLFormatter,
+                                                       ])
+    add_filter "/spec/"
+  end
 end
 
 require "qiita-markdown"