After this change Node.js installation is fine, but Grunt fails with Invalid API_KEY provided, but it's okay because it relies on a private key that pull requests don't have access to.

Nice, thank you !
Tested with my own saucelabs key, everything is ok.
Also, thanks to @SheetJSDev for imaya/zlib.js#27 :)

@dduponchel @Mithgol there is a way to encrypt the sauce labs key so that you can include it in the .travis.yml. Jump down to the "Securely Send Travis CI your Sauce Credentials" section in https://saucelabs.com/opensource/travis

@SheetJSDev That's already been done but secure keys aren't decrypted on pull requests, see my comment here.

@Stuk Can the tests be made to report “it's okay” instead of running a real Sauce test when they encounter missing secure variables? To work around instant failures of Sauce tests in pull requests.

@Mithgol fixed in 88d1b6b

Thanks.