Switch to using Python 3.8 on travis (also update dist for that); sti…

…ll testing 2.7, 3.6, 3.7 with crucial tests

.travis.yml

@@ -1,15 +1,15 @@
-dist: xenial
+dist: bionic
 sudo: false
 language: python
 # Working towards support https://numpy.org/neps/nep-0029-deprecation_policy.html
 python:
-  - "3.7"
+  - "3.8"
 env: #split tests
   global:
     - REQUIRES_PYNBODY=false
     - REQUIRES_ASTROPY=false
     - REQUIRES_ASTROQUERY=false
-    - PYTHON_COVREPORTS_VERSION=3.7 # Version for which reports are uploaded
+    - PYTHON_COVREPORTS_VERSION=3.8 # Version for which reports are uploaded
   matrix:
     - TEST_FILES='tests/ --ignore=tests/test_qdf.py --ignore=tests/test_pv2qdf.py --ignore=tests/test_diskdf.py --ignore=tests/test_orbit.py --ignore=tests/test_streamdf.py --ignore=tests/test_streamgapdf.py --ignore=tests/test_evolveddiskdf.py --ignore=tests/test_quantity.py --ignore=tests/test_nemo.py --ignore=tests/test_amuse.py --ignore=tests/test_coords.py --ignore=tests/test_jeans.py --ignore=tests/test_orbits.py' REQUIRES_PYNBODY=true
     - TEST_FILES='tests/test_quantity.py tests/test_coords.py' REQUIRES_ASTROPY=true # needs to be separate for different config
@@ -18,12 +18,14 @@ env: #split tests
     - TEST_FILES='tests/test_diskdf.py'
     - TEST_FILES='tests/test_qdf.py tests/test_pv2qdf.py tests/test_streamgapdf.py'
     - TEST_FILES='tests/test_streamdf.py'
-matrix: # only run crucial tests for python 2.7, 3.6
+matrix: # only run crucial tests for python 2.7, 3.6, 3.7
   include:
     - python: "2.7"
       env: TEST_FILES='tests/test_orbit.py tests/test_orbits.py' REQUIRES_PYNBODY=true REQUIRES_ASTROPY=true REQUIRES_ASTROQUERY=true
     - python: "3.6"
       env: TEST_FILES='tests/test_orbit.py tests/test_orbits.py' REQUIRES_PYNBODY=true REQUIRES_ASTROPY=true REQUIRES_ASTROQUERY=true
+    - python: "3.7"
+      env: TEST_FILES='tests/test_orbit.py tests/test_orbits.py' REQUIRES_PYNBODY=true REQUIRES_ASTROPY=true REQUIRES_ASTROQUERY=true
 addons:
   apt:
     packages: