Update node version in .travis.yml after MDL-66109 upstream change.

.travis.yml

@@ -27,8 +27,8 @@ env:
 
 before_install:
   - phpenv config-rm xdebug.ini
-  - nvm install 8.9
-  - nvm use 8.9
+  - nvm install 14 # moodle-plugin-ci still uses 8.9, but Moodle core switched to 14 in MDL-66109.
+  - nvm use 14
   - cd ../..
   - composer create-project -n --no-dev --prefer-dist blackboard-open-source/moodle-plugin-ci ci dev-master
   - export PATH="$(cd ci/bin; pwd):$(cd ci/vendor/bin; pwd):$PATH"