Kotlin: Fix typo

Author: igfoo

java/ql/integration-tests/all-platforms/kotlin/path_transformer/test.py

@@ -11,4 +11,4 @@
 exists = list(map(os.path.exists, files))
 if exists != [True] * 2:
     print(exists)
-    raise Exception("Didn't get expected filed")
+    raise Exception("Didn't get expected files")