Update CHANGE_LOG for 0.50
Update CHANGE_LOG for 0.50

As title.

gmarkall/numba,IntelLabs/numba,sklam/numba,cpcloud/numba,gmarkall/numba,stonebig/numba,stuartarchibald/numba,cpcloud/numba,stonebig/numba,numba/numba,cpcloud/numba,stuartarchibald/numba,numba/numba,stonebig/numba,sklam/numba,stonebig/numba,numba/numba,IntelLabs/numba,IntelLabs/numba,sklam/numba,seibert/numba,seibert/numba,sklam/numba,cpcloud/numba,gmarkall/numba,stonebig/numba,stuartarchibald/numba,sklam/numba,seibert/numba,seibert/numba,cpcloud/numba,gmarkall/numba,IntelLabs/numba,seibert/numba,IntelLabs/numba,stuartarchibald/numba,gmarkall/numba,numba/numba,stuartarchibald/numba,numba/numba