[Piglit] [PATCH] travis: reflect new best-practice travis-ci configuration

[Rhys Kidd]

Travis-CI has or will shortly make in early December 2018 a number of beneficial
changes to their Linux continuous integration testing infrastructure [0][1].
An accompanying benefit of this change is that Ubuntu Xenial (16.04 LTS) is now
supported.

The benefits for piglit are primarily:
* Testing against a more modern, supported Ubuntu Xenial (16.04 LTS). [2]
* Removal of a corner-case for Python 3.7, makes testing more consistent.
* Modest speed improvements from Travis-CI move to Linux infrastructure combined
  into one (virtualized), from two previously (virtualized and container-based).

[0] https://blog.travis-ci.com/2018-10-04-combining-linux-infrastructures
[1] https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration
[2] https://docs.travis-ci.com/user/reference/xenial/

Signed-off-by: Rhys Kidd <rhyskidd at gmail.com>
---
 .travis.yml | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index 45b23f009..3043cd4ca 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,10 @@
-sudo: false
-os: linux
 language: python
+
+os: linux
+
+# Use Ubuntu Xenial (16.04 LTS) environment.
+dist: xenial
+
 cache:
   - ccache
   - pip
@@ -23,7 +27,6 @@ matrix:
       env: TOX_ENV="py36-{generator,noaccel,accel-nix,streams}"
     - python: 3.7
       env: TOX_ENV="py37-{generator,noaccel,accel-nix,streams}"
-      dist: xenial    # required for Python 3.7 (travis-ci/travis-ci#9069)
     - env: BUILD=cmake
 
 install:
-- 
2.19.1