Updates for release 3.4

Author: xavierleroy

Changelog

@@ -1,4 +1,4 @@
-Release 3.4,
+Release 3.4, 2018-09-17
 =======================
 
 Bug fixing:

doc/index.html

@@ -24,7 +24,7 @@
 
 <H1 align="center">The CompCert verified compiler</H1>
 <H2 align="center">Commented Coq development</H2>
-<H3 align="center">Version 3.3, 2018-05-30</H3>
+<H3 align="center">Version 3.4, 2018-09-17</H3>
 
 <H2>Introduction</H2>