Point to curvlinops master branch in setup.cfg

[wiseodd]

Useful when people do

pip install git+https://git@github.com/aleximmer/laplace

or

git clone pip install https://github.com/aleximmer/laplace
cd laplace
pip install -e .

Addressing #150

[runame]

We can do this for now, but should switch back to the latest released version once we create a new laplace-torch release.