Change `--build` to use an absolute path #170

Job	Run time
Rustfmt	10s
Test (ubuntu-latest, stable)	21s
Test (ubuntu-latest, beta)	19s
Test (ubuntu-latest, nightly)	20s
Test (macos-latest, stable)	1m 2s
Test (macos-latest, beta)	37s
Test (macos-latest, nightly)	1m 2s
Test (windows-latest, stable)	1m 55s
Test (windows-latest, beta)	1m 54s
Test (windows-latest, nightly)	1m 52s
Test Cross Compile - aarch64-apple-ios	44s
Test Cross Compile - aarch64-unknown-linux-gnu	42s
Test Cross Compile - arm-unknown-linux-gnueabihf	43s
Test Cross Compile - mips-unknown-linux-gnu	10s
Test Cross Compile - mips64-unknown-linux-gnuabi64	12s
Test Cross Compile - mips64el-unknown-linux-gnuabi64	14s
Test Cross Compile - mipsel-unknown-linux-gnu	11s
Test Cross Compile - powerpc-unknown-linux-gnu	37s
Test Cross Compile - s390x-unknown-linux-gnu	48s
Test Cross Compile - x86_64-unknown-linux-musl	50s
Test Cross Compile - aarch64-unknown-linux-musl	49s
Test Cross Compile - x86_64-pc-windows-gnu	1m 12s
Test Cross Compile - x86_64-unknown-freebsd	45s
Test Cross Compile - x86_64-unknown-netbsd	46s
Test Cross Compile - x86_64-sun-solaris	44s
Test Cross Compile - x86_64-unknown-illumos	44s
	19m 43s

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