added alias: f -> git fetch --prune

gitconfig

@@ -75,6 +75,7 @@
 	a = add
 	c = commit
 	d = diff
+	f = fetch --prune
 	p = push --verbose
 	s = status
 	t = for-each-ref --sort taggerdate --format '%(taggerdate:iso) %(objectname) %(tag)' refs/tags