don't recommend sudo, add npm install to test command

[OmgImAlexis]

It's not a good idea to recommend using sudo to npm install -g as it can cause permission issues. If the user can't install it without sudo they can then try it themselves. Npm itself does recommend avoiding use of sudo as well.

Also added npm install to the test commands since it actually needs to be run locally before tap will work.

module.js:472
    throw err;
    ^

Error: Cannot find module 'tap'
    at Function.Module._resolveFilename (module.js:470:15)
    at Function.Module._load (module.js:418:25)
    at Module.require (module.js:498:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/Users/xo/code/node-cleanup/tests/multiple.js:3:9)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)
    at Function.Module._load (module.js:439:3)

[jtlapp]

Thank you!