regex: allow "." to be used as a simple quantifier

Fix issue json-schema-org#1469

jsonschema-core.md

@@ -403,7 +403,8 @@ tokens:
 - simple character classes ("[abc]"), range character classes ("[a-z]");
 - complemented simple character classes ("[^abc]"),
   complemented range character classes ("[^a-z]");
-- simple quantifiers: "+" (one or more), "*" (zero or more), "?" (zero or one),
+- simple quantifiers: "." (any character except line terminator),
+  "+" (one or more), "*" (zero or more), "?" (zero or one),
   and their lazy versions ("+?", "*?", "??");
 - range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at least x, at most
   y, occurrences), {x,} (x occurrences or more), and their lazy versions;