Update travis node to 12; drop python <3.6 testing

.travis.yml

@@ -2,11 +2,9 @@
 language: python
 dist: xenial
 python:
- - 2.7
- - 3.4
- - 3.5
  - 3.6
  - 3.7
+ - 3.8
 addons:
  apt_packages:
  - pandoc
@@ -21,6 +19,7 @@ before_install:
  - 'if [[ $GROUP == python ]] ; then bash ./scripts/travis_before_install_py.sh ; fi'
  - 'if [[ $GROUP == doc ]] ; then bash ./scripts/travis_before_install_py.sh ; fi'
  - 'if [[ $GROUP == spec ]] ; then bash ./scripts/travis_before_install_py.sh ; fi'
+ - 'if [[ $GROUP == js ]] ; then nvm install 12 ; fi'
 install:
  - 'if [[ $GROUP == python ]] ; then bash ./scripts/travis_install_py.sh ; fi'
  - 'if [[ $GROUP == doc ]] ; then bash ./scripts/travis_install_py.sh ; fi'
@@ -38,6 +37,6 @@ matrix:
  - python: 3.6
  env: GROUP=doc
  - python: 3.6
- env: GROUP=js BROWSER=firefox TRAVIS_NODE_VERSION=6.11.0
+ env: GROUP=js BROWSER=firefox TRAVIS_NODE_VERSION=10.15.3
 after_success:
  - coveralls