Add missing build dependency.

Alexis Lopez Zubieta · Alexis Lopez Zubieta · commit 3138d130f5ab · 2018-10-04T20:43:05.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -15,6 +15,7 @@ addons:
     - qtbase5-dev
     - qtdeclarative5-dev-tools
     - qtdeclarative5-dev
+    - qtwebengine5-dev
     - cmake
 
 script:
