Fix license badge to match current practice #138

Job	Run time
cargo check (msrv) (wasm32)	33s
cargo clippy (wasm32)	42s
cargo check (msrv) (windows-latest)	1m 20s
cargo clippy (windows-latest)	1m 25s
cargo check (msrv) (macos-latest)	1m 0s
cargo clippy (macos-latest)	52s
cargo check (msrv) (ubuntu-latest)	33s
cargo doc	28s
cargo clippy (ubuntu-latest)	35s
formatting	29s
cargo test (wasm32)	37s
cargo test (windows-latest)	1m 28s
cargo test (macos-latest)	41s
typos	4s
cargo test (ubuntu-latest)	31s
	11m 18s

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