Make OAuthAccessTokenParser objc compatible

[bckr]

Description:

With merging #79 we accidentally broke objc compatibility because of the newly introduced OAuthAccessTokenParser that exposes the Result type in our initializer.

Proposed solution:

I've changed the signature of OAuthAccessTokenParser to throw instead of returning Result

@objc public protocol OAuthAccessTokenParser {
    func parse(data: NSData) throws -> OAuthAccessToken
}

fyi: @poislagarde

[Stengo]

Looks good to me. I think this is the nicest solution to restore objc compatibility 👍

[SusannProszak]

👍 looks good