README.rst: attempt to make clickable travis-ci image this time

Signed-off-by: Sergei Trofimovich <siarheit@google.com>

README.rst

 Gentoo Haskell project
 **********************
 
+travis.ci:
+
 .. image:: https://travis-ci.org/gentoo-haskell/gentoo-haskell.svg?branch=master
+    :target: https://travis-ci.org/gentoo-haskell/gentoo-haskell
 
 Quickest start
 ==============