test(docs): install -g npm@7 (#2912)

* test: install npm@7

* test: change npm to yarn

* Revert "test: change npm to yarn"

This reverts commit f31e647.

* test: install -g npm@7

Co-authored-by: 0618 <[email protected]>

Author: 0618

amplify.yml

@@ -33,7 +33,7 @@ applications:
           commands:
             - nvm install 16.13 # NodeJS 16.13+ is the latest version that Amplify Hosting supports
             - nvm use 16
-            - npm install npm@7 # TODO: remove this line once update @angular-devkit packages.
+            - npm install -g npm@7 # TODO: remove this line once update @angular-devkit packages.
             - export NODE_OPTIONS="--max-old-space-size=8192"
             - npm install
             - npm install wait-on