change nodee version code example

Example 1: change node version

Usage:
nvm install <version>       Download and install a <version>
nvm use <version>           Modify PATH to use <version>
nvm ls                      List versions (installed versions are blue)

Example 2: how to change node version

nvm use --delete-prefix $NODE_VERSION

example:
nvm use --delete-prefix v8.9.4