Use of impl Into<String> in RequestBuilder::bearer_auth

[fgimian]

Hey there, great job on this library, thanks for all your hard work! 😄

I was wondering why the bearer_auth function uses token: impl Into<String>. This would potentially result in unnecessary allocation of a String just for use in the Authorization header.

Is there any reason AsRef<str> could not be used instead?

Cheers
Fotis