Tweaks to make coverage

Makefile

@@ -70,7 +70,7 @@ test:
 coverage:
 	rm -f gcov/*.gcda gcov/*.gcno .coverage
 	mkdir -p gcov
-	cd gcov && gcc -coverage -o ../bin/vplanet ../src/*.c -lm
+	gcc -coverage -o bin/vplanet src/*.c -lm
 	python -m pytest --tb=short tests --junitxml=junit/test-results.xml
 	lcov --capture --directory gcov --output-file .coverage
 	genhtml .coverage --output-directory gcov/html