Add Stan to contributors
Add Stan to contributors

As title.
stuartarchibald/numba,stuartarchibald/numba,jriehl/numba,numba/numba,cpcloud/numba,stuartarchibald/numba,numba/numba,stonebig/numba,sklam/numba,gmarkall/numba,IntelLabs/numba,seibert/numba,seibert/numba,jriehl/numba,seibert/numba,stonebig/numba,jriehl/numba,numba/numba,stonebig/numba,jriehl/numba,stuartarchibald/numba,seibert/numba,numba/numba,cpcloud/numba,cpcloud/numba,gmarkall/numba,stonebig/numba,gmarkall/numba,cpcloud/numba,IntelLabs/numba,IntelLabs/numba,sklam/numba,stuartarchibald/numba,sklam/numba,jriehl/numba,numba/numba,IntelLabs/numba,sklam/numba,cpcloud/numba,stonebig/numba,seibert/numba,sklam/numba,gmarkall/numba,gmarkall/numba,IntelLabs/numba