tests: use 'ps auxf'

tests/unit/50_init_2.bats

@@ -14,7 +14,7 @@ teardown() {
 
 @test "(init) dockerfile no tini" {
   deploy_app zombies-dockerfile-no-tini
-  run ps ax
+  run ps auxf
   echo "output: $output"
   assert_output_contains "<defunct>" "0"
 }