update coveralls

because, coveralls(0.5.7) has `warning: File.exists?`

Author: takkanm

Gemfile

@@ -17,7 +17,7 @@ end
 group :test do
   gem "addressable", "~> 2.3.6", :platforms => [:ruby_18]
   gem "childlabor"
-  gem "coveralls", ">= 0.5.7"
+  gem "coveralls", ">= 0.8.19"
   gem "json", "< 2" # This is to support Ruby 1.8 and 1.9
   gem "mime-types", "~> 1.25", :platforms => [:jruby, :ruby_18]
   gem "rest-client", "~> 1.6.0", :platforms => [:jruby, :ruby_18]