[master] 6c625090a Revert "travis: Our svg bits require graphviz"

[Dag Haavi Finstad]

commit 6c625090a1ad51a6abd6ead5dad735fda75861ad
Author: Dag Haavi Finstad <daghf at varnish-software.com>
Date:   Thu Dec 6 10:48:50 2018 +0100

    Revert "travis: Our svg bits require graphviz"
    
    This reverts commit 5b6a4e5600ebf37fb3a7f46020e38da4cc8994ae.

diff --git a/.travis.yml b/.travis.yml
index 311ebd559..8d31d9e04 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -24,7 +24,6 @@ addons:
     packages:
       - python-docutils
       - python-sphinx
-      - graphviz
   homebrew:
     packages:
       - docutils