Fix documentation typo: "turn of listeners"

[AndrewSouthpaw]

In specifying the optional file parameter for the DELETE, GET, POST, and PUT methods, the documentation reads:

Optional; specify a filesystem path to save the response body as file instead of Buffer. Passing null turns of the data listeners

I think it should read (emphasis mine):

Optional; specify a filesystem path to save the response body as file instead of Buffer. Passing null turns off the data listeners

[SaltwaterC]

Yep. Non-native speaker is non-native. Merged your changes into the future branch and pushed the actual changes to gh-pages. It will appear as merged, per GitHub, once the master branch is updated with a new release. Thanks.