chore: fix links in Cargo.toml #84

Job	Run time
doc	19s
check (nightly, x86_64-unknown-none)	16s
check (stable, riscv64gc-unknown-none-elf)	14s
check (nightly, x86_64-unknown-linux-gnu)	40s
check (stable, x86_64-unknown-none)	12s
check (stable, x86_64-unknown-linux-gnu)	15s
check (stable, aarch64-unknown-none-softfloat)	12s
check (nightly, riscv64gc-unknown-none-elf)	18s
check (nightly, --all-features, riscv64gc-unknown-none-elf)	26s
check (nightly, aarch64-unknown-none-softfloat)	17s
check (nightly, --all-features, aarch64-unknown-none-softfloat)	26s
check (nightly, --all-features, x86_64-unknown-none)	27s
check (nightly, --all-features, x86_64-unknown-linux-gnu)	52s
	4m 54s

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