chore: Release libwebp-sys2 version 0.1.8 #60

Job	Run time
test (stable, 0.4.4, build)	51s
test (stable, 0.5.2, build)	1m 23s
test (stable, 1.0.3, build)	2m 8s
test (stable, 1.1.0, build)	1m 59s
test (stable, 1.2.0, build)	1m 50s
test (stable, 0.6.1, distr)	37s
test (stable, 1.2.0, bundled)	3m 39s
test (1.34.0, 1.2.0, build)	3m 27s
test (beta, 1.2.0, build)	1m 49s
test (nightly, 1.2.0, build)	2m 18s
test (nightly, 1.2.0, build, extern-types,)	1m 49s
	21m 50s

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