Wrong docker image in readme

[tenjaa]

Hey,
I was playing around with this resource and had some issues in the beginning, because it says the docker image can be found under: concourse-git-bitbucket-pr
But this image does not exist, it should be concourse-git-bitbucket-pr-resource :)

And it should be base_url instead of url in the documentation

And I cannot use this resource when there is a whitespace in my password