Download grcov binary instead of building it.

Makefile

@@ -9,22 +9,23 @@ build:
 	maturin develop
 
 test:
-	# install dependencies
-	rustup component add llvm-tools-preview
-	cargo install grcov
-
 	# clean test coverage directory
 	rm -rf ./target/test_coverage
 	mkdir -p ./target/test_coverage
 
+	# install dependencies
+	rustup component add llvm-tools-preview
+	curl -sL https://github.com/mozilla/grcov/releases/download/v0.8.10/grcov-x86_64-unknown-linux-gnu.tar.bz2 | tar jxf - -C "./target/test_coverage"
+	chmod +x ./target/test_coverage/grcov
+
 	# run tests
 	CARGO_INCREMENTAL=0 RUSTFLAGS='-Cinstrument-coverage' LLVM_PROFILE_FILE='target/test_coverage/profraw/cargo-test-%p-%m.profraw' cargo test --verbose
 
 	# generate html coverage report
-	grcov . --binary-path ./target/debug/deps/ -s . -t html --branch --ignore-not-existing --ignore '../*' --ignore "/*" -o target/test_coverage/html
+	./target/test_coverage/grcov . --binary-path ./target/debug/deps/ -s . -t html --branch --ignore-not-existing --ignore '../*' --ignore "/*" -o target/test_coverage/html
 
 	# generate lcov coverage report
-	grcov . --binary-path ./target/debug/deps/ -s . -t lcov --branch --ignore-not-existing --ignore '../*' --ignore "/*" -o target/test_coverage/tests.lcov
+	./target/test_coverage/grcov . --binary-path ./target/debug/deps/ -s . -t lcov --branch --ignore-not-existing --ignore '../*' --ignore "/*" -o target/test_coverage/tests.lcov
 
 
 .PHONY: precommit build test