Update cmake_minimum_required to 3.9 #81

Job	Run time
clang-sanitizers (,thread)	1m 11s
clang-sanitizers (,address,undefined)	1m 25s
linux-shared-libs	1m 3s
linux-compiler-compat (clang-3)	1m 2s
linux-compat (manylinux1-x64)	42s
linux-compiler-compat (clang-6)	4m 31s
windows	2m 0s
linux-compat (manylinux1-x86)	39s
linux-compiler-compat (clang-8)	4m 46s
windows-shared-libs	1m 45s
linux-compat (manylinux2014-x64)	57s
linux-compiler-compat (clang-9)	4m 42s
linux-compat (manylinux2014-x86)	47s
linux-compiler-compat (clang-10)	1m 11s
windows-vc14 (x86)	2m 42s
linux-compiler-compat (clang-11)	1m 15s
linux-compat (fedora-34-x64)	42s
windows-vc14 (x64)	1m 14s
linux-compiler-compat (gcc-4.8)	46s
linux-compat (opensuse-leap)	41s
linux-compiler-compat (gcc-5)	52s
linux-compat (rhel8-x64)	37s
linux-compiler-compat (gcc-6)	51s
linux-compat (al2-x64)	37s
downstream	39m 1s
linux-compiler-compat (gcc-7)	52s
linux-compiler-compat (gcc-8)	58s
macos	34s
macos-x64	41s
windows-app-verifier	1m 44s
	1h 20m 48s

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