Bump version to v2.0.0-rc12 #313

Job	Run time
aarch64-unknown-linux-gnu	2m 59s
aarch64-unknown-linux-musl	3m 9s
x86_64-unknown-linux-gnu	1m 41s
x86_64-unknown-linux-musl	3m 0s
arm-unknown-linux-gnueabi	3m 3s
arm-unknown-linux-gnueabihf	3m 8s
armv7-unknown-linux-gnueabihf	3m 2s
powerpc-unknown-linux-gnu	3m 1s
powerpc64-unknown-linux-gnu	3m 8s
powerpc64le-unknown-linux-gnu	2m 58s
s390x-unknown-linux-gnu	3m 10s
aarch64-apple-darwin	2m 53s
x86_64-apple-darwin	2m 20s
x86_64-pc-windows-msvc	5m 30s
aarch64-pc-windows-msvc	5m 6s
publish	1m 1s
	49m 9s

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