Include npm version when displaying results of switch.

[ajcrites]

When running nvm use, successful changing of versions lists the new node version. The npm version may also be switched, but this is not listed.

This commit updates nvm to display the npm version that was switched to alongside the node version

[ljharb]

Not a bad idea at all! This will definitely fail tests, so please do update the relevant test files with the appropriate message.

[ljharb]

echo -n isn't supported in sh (although it is supported in all other supported shells). Instead of using that, could we capture the npm version in a variable before the if/else, and interpolate that into a single echo command?

[ljharb]

Also, please do note that versions of node older than v0.2.3 don't support npm at all, so we'd need to make sure that the npm text was only displayed if nvm_has "npm" after switching.

[ajcrites]

I missed this in the tests and I didn't actually think to run the tests. Silly me.

Fast tests pass for me. Slow tests do not pass on my system -- not even in the master branch (only the nvm_do_install test seems to fail).

I tried in both zsh and bash, disabling .npmrc and had not run nvm beforehand.

I was also not able to install 0.2.2 to test lack of npm specifically.

[ljharb]

Not all the tests run reliably locally, so let's see how travis-ci does with them.

[ljharb]

Sorry for the delay - this looks great, thanks!