fix typo (still -> install) #866

Job	Run time
linux-check-and-test-armv7	2m 0s
rustfmt-check	8s
ubuntu-test	54s
clippy-test	1m 5s
android-check	46s
android-apk-build	2m 0s
asmjs-wasm32-test (wasm32-unknown-emscripten)	1m 8s
cargo-publish	0s
ios-build	2m 58s
macos-test	51s
wasm32-bindgen-test (wasm32-unknown-unknown)	25s
wasm32-wasi-test (wasm32-wasi)	15s
windows-test (x86_64)	3m 9s
wasm-beep-build	52s
windows-test (i686)	2m 7s
	18m 38s

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