refactor: replace deprecated String.prototype.substr()

.substr() is deprecated so we replace it with .slice() which works similarily but isn't deprecated
Signed-off-by: Tobias Speicher <rootcommander@gmail.com>

lib/help.js

@@ -387,8 +387,8 @@ class Help {
     const columnWidth = width - indent;
     if (columnWidth < minColumnWidth) return str;
 
-    const leadingStr = str.substr(0, indent);
-    const columnText = str.substr(indent);
+    const leadingStr = str.slice(0, indent);
+    const columnText = str.slice(indent);
 
     const indentString = ' '.repeat(indent);
     const regex = new RegExp('.{1,' + (columnWidth - 1) + '}([\\s\u200B]|$)|[^\\s\u200B]+?([\\s\u200B]|$)', 'g');