Fix travis exclude for self mutation

Rakefile

@@ -4,9 +4,10 @@ require 'devtools'
 
 Devtools.init_rake_tasks
 
-
 # Mutant self test is to slow for travis. Fast enough for circle.
 if ENV['TRAVIS']
+  Rake.application.load_imports
+
   task('metrics:mutant').clear
   namespace :metrics do
     task :mutant => :coverage do