typo in announcements (2.11.1 vs. 2.11.2)

[li...@rhsoft.net]

http://www.postfix.org/announcements.html
* link correct http://www.postfix.org/announcements/postfix-2.11.2.html
* 2.11.1 in the text should be 2.11.2

October 13, 2014: Postfix stable release 2.11.1 and legacy releases 
2.10.4, 2.9.10, and 2.8.18.

May 7, 2014: Postfix stable release 2.11.1.