Update Travis to build n-1 python versions

Updated devnotes for testing and release process

.travis.yml

@@ -10,9 +10,8 @@ language: python
 matrix:
   include:
     - python: 2.7
-    - python: 3.5
-    - python: 3.6
-    - python: 3.7
+    - python: 3.8
+    - python: 3.9
       dist: xenial
       sudo: true
 script: tox

docs/devnotes.rst

@@ -154,6 +154,8 @@ This assumes you have virtualenvwrapper, git, and appropriate python versions in
     pip install path/to/nipyapi-0.3.1-py2.py3-none-any.whl  # for example
     # Run appropriate tests, such as usage tests etc.
     deactivate
+    Push changes to Github
+    Check build on TravisCI
     # You may have to reactivate your original virtualenv
     twine upload dist/*
     # You may get a file exists error, check you're not trying to reupload an existing version