Update PURL-SPECIFICATION.rst

Signed-off-by: Philippe Ombredanne <pombredanne@aboutcode.org>

Author: pombredanne

PURL-SPECIFICATION.rst

@@ -295,7 +295,7 @@ full case mapping defined in
 `Section 3.13.2 of the Unicode Standard <https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-3/#G34078>`_.
 
 When applied to the ASCII character set, this operation converts uppercase
-Latin letters (``A``–``Z``) to their corresponding lowercase forms (``a``–``z``).
+Latin letters (``A to Z``) to their corresponding lowercase forms (``a to z``).
 All other ASCII characters remain unchanged.
 
 How to build ``purl`` string from its components