Update to commit f6a88ce from git@github.com:gedex/wp-slack.git

Includes the following commit(s):

commit f6a88cead6b4c81495e9f5d8c0f14d70ecb31eda
Author: Akeda Bagus <akeda@x-team.com>

    Fix typo.

M	includes/plugin.php
M	readme.md
M	readme.txt


git-svn-id: https://plugins.svn.wordpress.org/slack/trunk@903000 b8457f37-d9ea-0310-8a92-e5e31aec5664