Define task for update dependency, clean dependency

Rakefile

@@ -14,4 +14,12 @@ task :test do
   sh 'bundle exec vim-flavor test'
 end
 
+task :updatedepends do
+  sh 'bundle update'
+end
+
+task :cleandepends do
+  sh 'bundle clean'
+end
+
 # vim: et sw=2 ts=2 sts=2: