Add release date for 3.4.7

Author: Legrandin

Changelog.rst

@@ -1,8 +1,8 @@
 Changelog
 =========
 
-3.4.7 (xx xxx 2017)
-+++++++++++++++++++++++
+3.4.7 (26 August 2017)
+++++++++++++++++++++++
 
 New features
 ------------

README.rst

@@ -73,7 +73,8 @@ All the code can be downloaded from `GitHub`_.
 News
 ----
 
-* **17 May 2017 (NEW)**. Bugfix release 3.4.6.
+* **26 Aug 2017 (NEW)**. Bugfix release 3.4.7.
+* 17 May 2017. Bugfix release 3.4.6.
 * 6 Feb 2017. Bugfix release 3.4.5.
 * 1 Feb 2017. Bugfix release 3.4.4.
 * 17 Oct 2016. Bugfix release 3.4.3.