Travis: removed libglui-dev package

* Not found by Travis.
* The Viewer plugin will not be built.

Author: Clement Champetier

.travis.yml

@@ -112,7 +112,7 @@ addons:
     - libyaml-dev
     # - libopenctl0.8
     - libcaca-dev
-    - libglui-dev
+    # - libglui-dev
     - libtinyxml-dev
     - yasm
     - libx264-dev