fix: ensure $ABRA_DIR/servers is 0600

Also remove deprecated folders while I'm here: `vendor` / `backup`

See toolshed/abra#580

tests/integration/dirs.bats

@@ -24,7 +24,7 @@ setup(){
   assert_success
 }
 
-@test "abra directory is created" {
+@test "abra directories are created" {
   run $ABRA app ls
 
   # NOTE(d1): no servers yet, so will fail. however, it will run the required
@@ -35,8 +35,9 @@ setup(){
   assert_exists "$ABRA_DIR"
   assert_exists "$ABRA_DIR/servers"
   assert_exists "$ABRA_DIR/recipes"
-  assert_exists "$ABRA_DIR/backups"
-  assert_exists "$ABRA_DIR/vendor"
 
   assert_not_exists "$ABRA_DIR/catalogue"
+
+  server_dir_perms=$(stat -c "%a" "$ABRA_DIR/servers")
+  assert_equal $server_dir_perms "600"
 }