Add zlib to travis

ChrisJefferson · ChrisJefferson · commit cdce5fc19a6f · 2018-06-05T11:03:15.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -12,6 +12,7 @@ addons:
   apt_packages:
     - libgmp-dev
     - libreadline-dev
+    - zlib1g-dev
 
 matrix:
   include:
