test: fix acceptance tests

examples/acceptance_tests/048/plutus.json

@@ -5,8 +5,7 @@
   },
   "validators": [
     {
-      "title": "foo",
-      "purpose": "spend",
+      "title": "foo.spend",
       "datum": {
         "title": "Data",
         "description": "Any Plutus data."

examples/acceptance_tests/048/validators/foo.ak

@@ -4,6 +4,8 @@ fn when_tuple(a: (Int, Int)) -> Int {
   }
 }
 
-pub fn spend(a: Data, b: Data, c) -> Bool {
-  when_tuple((4, 1)) == 4
+validator spend {
+  fn(a: Data, b: Data, c) -> Bool {
+    when_tuple((4, 1)) == 4
+  }
 }