travis.yml: Modernise.

vpelletier · vpelletier · commit 734a0096852d · 2020-05-07T11:02:22.000Z
sudo is deprecated and causing a warning.
dist is super outdated now, and its gcc failing to build current libusb1.
os is missing and causing a warning.
diff --git a/.travis.yml b/.travis.yml
@@ -1,5 +1,4 @@
-sudo: required
-dist: trusty
+os: linux
 language: python
 python:
 - "2.7"
