Fix using Node.js

.travis.yml

@@ -1,8 +1,12 @@
 language: php
-
-node_js: 10
 php: 7.3
 
+before_install:
+- nvm install 10
+- node -v
+- curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version version-number
+- export PATH="$HOME/.yarn/bin:$PATH"
+
 install:
 - composer install --no-dev
 - rm -rf vendor/bin