fix bin/tests target causing make errors

Signed-off-by: Niklas Eiling <niklas.eiling@eonerc.rwth-aachen.de>

Makefile

 #MIT License...
 
-.PHONY: all cuda-gdb libtirpc gpu cpu tests clean install install-cpu bin/tests
+.PHONY: all cuda-gdb libtirpc gpu cpu tests clean install install-cpu
 
 all: cpu install
 
@@ -46,7 +46,7 @@ bin:
 	mkdir bin
 
 bin/tests: bin tests
-	ln -s ../tests/bin bin/tests
+	ln -sf ../tests/bin bin/tests
 
 bin/cricket-client.so: bin
 	$(MAKE) -C cpu cricket-client.so