Change coverage output format to json

Author: Umekawa

spec/spec_helper.rb

@@ -1,7 +1,16 @@
 # frozen_string_literal: true
 
 require 'simplecov'
-SimpleCov.start
+require 'simplecov_json_formatter'
+
+SimpleCov.start do
+  SimpleCov.formatters = [
+    SimpleCov::Formatter::JSONFormatter,
+    SimpleCov::Formatter::HTMLFormatter
+  ]
+
+  add_filter '/spec/'
+end
 
 require 'ruboty/github'
 require 'webmock/rspec'