Update .travis.yml

Author: dcwhite

.travis.yml

@@ -20,11 +20,11 @@ matrix:
     - os: linux
       dist: xenial
       compiler: clang
-      env: PYTHON_VERSION=3.5.6 OSPRAY_BUILD=OFF QT5=ON
+      env: PYTHON_VERSION=3.6.7 OSPRAY_BUILD=OFF QT5=OFF
     - os: linux
       dist: bionic
       compiler: clang
-      env: PYTHON_VERSION=3.5.6 OSPRAY_BUILD=OFF QT5=ON
+      env: PYTHON_VERSION=3.5.6 OSPRAY_BUILD=OFF QT5=OFF
     - os: osx
       osx_image: xcode7.3
       env: PYTHON_VERSION=3.5.6 OSPRAY_BUILD=OFF QT5=OFF