[ticket/14970] Try using newer node version

PHPBB3-14970

travis/check-stylesheet.sh

@@ -18,6 +18,20 @@ NOTESTS=$3
 if [ "$NOTESTS" == '1' ]
 then
 	cd phpBB
+	# Define a node version.
+	TRAVIS_NODE_VERSION="4"
+
+	# Clear out whatever version of NVM Travis has.
+	# Their version of NVM is probably old.
+	rm -rf ~/.nvm
+	# Grab NVM.
+	git clone https://github.com/creationix/nvm.git ~/.nvm
+	# Checkout the latest stable tag.
+	# Note that you can just hardcode a preferred version here.
+	(cd ~/.nvm && git checkout `git describe --abbrev=0 --tags`)
+	# Install the desired version of Node
+	source ~/.nvm/nvm.sh
+	nvm install $TRAVIS_NODE_VERSION
 	npm install -g
 	npm install
 	stylelint --config ../.stylelintrc "styles/prosilver/theme/*.css"