Remove env var LFS_SCHEME in readme
Remove env var LFS_SCHEME in readme

Default LFS_SCHEME is http, cc #17, #20
github/lfs-test-server,github/lfs-test-server,iSC-Labs/lfs-test-server,iSC-Labs/lfs-test-server,Yopai/lfs-test-server,jezell/lfs-test-server,Yopai/lfs-test-server,jezell/lfs-test-server