Correct regex for metadata 'name' format

The current regex permits strings that end in the newline character,
which is counter to what the description for the field states ("ASCII
letters and numbers, period, underscore and hyphen").

This updates the rexex to use `\Z` instead of `$` to match at the end of
the string and exclude newline characters.

Author: di

source/specifications/name-normalization.rst

@@ -17,7 +17,7 @@ underscore and hyphen. It must start and end with a letter or number.
 This means that valid project names are limited to those which match the
 following regex (run with :py:data:`re.IGNORECASE`)::
 
-    ^([A-Z0-9]|[A-Z0-9][A-Z0-9._-]*[A-Z0-9])$
+    ^([A-Z0-9]|[A-Z0-9][A-Z0-9._-]*[A-Z0-9])\Z
 
 
 .. _name-normalization: