Bump version to v0.6.7 #105

Job	Run time
linux (x86_64-unknown-linux-gnu)	4m 58s
macos-aarch64	3m 40s
linux (i686-unknown-linux-gnu)	7m 29s
linux-cross (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	6m 6s
macos-x86_64	7m 38s
linux-cross (armv7-unknown-linux-gnueabihf, armv7)	5m 22s
musllinux (x86_64-unknown-linux-musl)	5m 1s
linux-cross (s390x-unknown-linux-gnu, s390x)	5m 36s
musllinux (i686-unknown-linux-musl)	4m 21s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	5m 35s
linux-cross (powerpc64le-unknown-linux-gnu, ppc64le, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	5m 32s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	5m 14s
sdist	4m 31s
linux-cross (powerpc64-unknown-linux-gnu, ppc64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	5m 21s
windows (x86_64-pc-windows-msvc, x64)	8m 15s
linux-cross (arm-unknown-linux-musleabihf, arm)	5m 21s
windows (i686-pc-windows-msvc, x86)	8m 38s
windows (aarch64-pc-windows-msvc, x64)	10m 31s
	1h 49m 9s

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