Fix a bug that was causing .vim.after to be removed after update

rake install/update was executing git clean with the -x flag that
force the removal of ignored files. Since .vim.after was listed
inside .gitignore, this was causing the file to be removed on
each update.
I don't think we need to remove ignored files since are all
temporary or user-specific configuration files that should
persist between updates.

Fixes #225

Rakefile

@@ -62,8 +62,8 @@ task :submodules do
 
     run %{
       cd $HOME/.yadr
-      git submodule foreach 'git fetch origin; git checkout master; git reset --hard origin/master; git submodule update --recursive; git clean -dfx'
-      git clean -dfx
+      git submodule foreach 'git fetch origin; git checkout master; git reset --hard origin/master; git submodule update --recursive; git clean -df'
+      git clean -df
     }
     puts
   end