Update license field following SPDX 2.1 license expression standard #1273

Job	Run time
Rustfmt	26s
Run wasm-bindgen crate tests (unix)	11m 42s
Verify that web-sys is compiled correctly	1m 39s
Check	1m 39s
Clippy	5m 57s
Run js-sys crate tests	3m 57s
Run native tests	3m 53s
Run wasm-bindgen crate tests with multithreading enabled	1m 53s
Run web-sys crate tests	8m 54s
build_benchmarks	1m 47s
build_examples	5m 16s
build_nightly	2m 13s
dist_linux_aarch64_gnu	3m 35s
dist_linux_x86_64_musl	3m 18s
dist_macos_x86_64	3m 37s
Build and test the deno example	1m 53s
Test TypeScript output of wasm-bindgen	1m 31s
Run UI compile-fail tests	1m 44s
Run wasm-bindgen-webidl crate tests	3m 56s
dist_macos_aarch64	3m 33s
dist_windows	4m 42s
doc_api	1m 41s
doc_book	12s
test_examples	3m 7s
deploy	1m 24s
	1h 23m 29s

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