fix 'make package'

Author: ry

Makefile

@@ -17,7 +17,7 @@ clean:
 	rm -f *.o http_parser.c test http_parser.tar
 
 package: http_parser.c
-	@mkdir -p /tmp/http_parser && \
+	@rm -rf /tmp/http_parser && mkdir /tmp/http_parser && \
 	cp README.md Makefile http_parser.c http_parser.rl \
 		http_parser.h test.c /tmp/http_parser && \
 	cd /tmp && \