Try to fix broken markdown of \ character.

CHANGELOG.md

@@ -4,7 +4,7 @@ This release adds the following new features:
 
 * [Regex for Advanced filter. It aims to solve search in bigger text fields, and using wildcards.
    A change to translations was made for adding info about regex and escaping characters
-   with \](https://github.com/wekan/wekan/pull/1702).
+   with \\](https://github.com/wekan/wekan/pull/1702).
 
 Thanks to GitHub users feuerball11 and xet7 for their contributions.