change active version nvm code example

Example 1: nvm set default

# Install the version that you would like 
nvm install 6.1.0

# Set 6.1.0 (or another version) as default
nvm alias default 6.1.0

Example 2: how to change node version

nvm use --delete-prefix $NODE_VERSION

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