luhn: non-digit at end is invalid

Author: bitfield

exercises/luhn/canonical-data.json

@@ -74,6 +74,14 @@
       },
       "expected": false
     },
+    {
+      "description": "valid strings with a non-digit added at the end become invalid",
+      "property": "valid",
+      "input": {
+        "value": "059a"
+      },
+      "expected": false
+    },
     {
       "description": "valid strings with punctuation included become invalid",
       "property": "valid",