Revert "Build: remove global install of latest npm since we want to u…

…se the paired node/npm version (#17134)"

This reverts commit 0b4d9c8.

.travis.yml

@@ -23,7 +23,7 @@ branches:
     - master
 
 before_install:
-  - nvm install
+  - nvm install --latest-npm
 
 env: PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true
 

bin/install-node-nvm.sh

@@ -69,6 +69,9 @@ fi
 echo -e $(status_message "Installing and updating NPM packages..." )
 npm install
 
+# Make sure npm is up-to-date
+npm install npm -g
+
 # There was a bug in NPM that caused changes in package-lock.json. Handle that.
 if [ "$TRAVIS" != "true" ] && ! git diff --no-ext-diff --exit-code package-lock.json >/dev/null; then
 	if ask "$(warning_message "Your package-lock.json changed, which may mean there's an issue with your NPM cache. Would you like to try and automatically clean it up?" )" N 10; then