Add missing build dependency.

Alexis Lopez Zubieta · Alexis Lopez Zubieta · commit 4cac80d1beda · 2018-10-04T20:31:32.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -13,6 +13,7 @@ addons:
     - g++
     - qt5-default
     - qtbase5-dev
+    - qtdeclarative5-dev
     - cmake
 
 script:
