Add missing build dependency.

Alexis Lopez Zubieta · Alexis Lopez Zubieta · commit 7afd3334baa9 · 2018-10-04T20:26:43.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -12,6 +12,7 @@ addons:
     - gcc
     - g++
     - qt5-default
+    - qtbase5-dev
     - cmake
 
 script:
