Try using latest master.

Author: ioquatix

Gemfile

@@ -4,5 +4,5 @@ source 'https://rubygems.org'
 gemspec
 
 group :test do
-gem "ruby-prof", "0.18.0", platform: :mri
+gem "ruby-prof", git: "https://github.com/ruby-prof/ruby-prof"
 end