Update travis node to 12; drop python <3.6 testing

Author: jasongrout

.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