Small fixes

[bhubr]

I tried to used the lib, and had an error when doing things such as:

const repositories = bitbucketApi.repositories.promised;
repositories.get(user, slug)
  .then(data => { // do something });

The error I got was:

get: Expected [object Arguments] arguments but received 0

It came from two things:

• The validateArgs function slices the args it receives. Apparently, doing it on an empty array doesn't work, but calling Array.prototype.slice does.
• When calling validateArgs from repositories.get, the order of arguments and the number of expected arguments was swapped.

So I felt free to submit this PR fixing both things. I had issues with running npm test though (Unexpected token import... meaning that sources were not babelified when running tests?).

[kristianmandrup]

Great! Thank you so much! I never got around to testing it fully, so thanks for catching these bugs. Feel free to submit more PRs in the future as you dive deeper. Also feel to suggest and submit PRs with API improvements. Cheers!

[bhubr]

You're welcome! Thanks for merging. I'll let you know if I get into other issues, if I use more features in my project. Cheers!