tf-a-commitlint: `nvm use` -> `nvm install`

NVM won't use the version specified unless it is already installed. When
we move to the next LTS then it won't be installed because the TF-A
Dockerfile only uses 14 (which is end-of-life April 2023).

On the other hand, `nvm install` will automatically run `nvm use` once
installation is complete.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: Ife2e0936df261ebfcdbb1989b0865d91b7fefd49
1 file changed