Restore regex format test from draft-03

Since it is now restored to the formats list.

Author: handrews

tests/draft7/optional/format.json

@@ -1,4 +1,20 @@
 [
+    {
+        "description": "validation of regular expressions",
+        "schema": {"format": "regex"},
+        "tests": [
+            {
+                "description": "a valid regular expression",
+                "data": "([abc])+\\s+$",
+                "valid": true
+            },
+            {
+                "description": "a regular expression with unclosed parens is invalid",
+                "data": "^(abc]",
+                "valid": false
+            }
+        ]
+    },
     {
         "description": "validation of date-time strings",
         "schema": {"format": "date-time"},