Fix composer remove phpunit/phpunit command

Author: thewilkybarkid

phpunit/phpunit/4.7/post-install.txt

@@ -3,5 +3,5 @@
 <bg=yellow;fg=black>                                                                                             </>
 
   * <fg=blue>Instead</>:
-    1. Remove it now: <comment>composer remove phpunit/phpunit</>
+    1. Remove it now: <comment>composer remove --dev phpunit/phpunit</>
     2. Use Symfony's bridge: <comment>composer require --dev phpunit</>