Clean up config file for Travis.

- remove obsolete "sudo" keyword
- remove old dev versions
- remove matrix

modified:   .travis.yml

.travis.yml

@@ -1,31 +1,12 @@
 language: python
-sudo: required
 dist: xenial
-matrix:
-  include:
-  - python: '3.6'
-  - python: 3.6-dev
-  - python: '3.7'
-  - python: 3.7-dev
-    dist: xenial
-    sudo: true
+python: 3.6
+python: 3.7
+python: 3.8-dev
+python: nightly
+allow_failures:
   - python: 3.8-dev
-    dist: xenial
-    sudo: true
   - python: nightly
-    dist: xenial
-    sudo: true
-  allow_failures:
-  - python: 3.6-dev
-  - python: 3.7-dev
-    dist: xenial
-    sudo: true
-  - python: 3.8-dev
-    dist: xenial
-    sudo: true
-  - python: nightly
-    dist: xenial
-    sudo: true
 install:
 - pip install -e .
 script: