Add link to commit by xet7 to CHANGELOG invitation code fix.

CHANGELOG.md

@@ -13,7 +13,7 @@ and fixes the following bugs:
 * [Whitespace trimming breaks Markdown code block indentation](https://github.com/wekan/wekan/issues/1288):
 * [Helper to list boards for user](https://github.com/wekan/wekan/pull/1327);
 * [Error after sending invitation and joining board: Exception while invoking method 'login' TypeError: Cannot read property 'loginDisabled' of undefined](https://github.com/wekan/wekan/issues/1331);
-* Invitation /sign-up page did not show input for invitation code.
+* [Invitation /sign-up page did not show input for invitation code](https://github.com/wekan/wekan/commit/99be745f0299b32a8a7b30204b43bff7fd5ba638).
 
 Thanks to Github users brooksbecton, milesibastos, nztqa, soohwa, thuanpq and xet7 for their contributions.