fix bitset (#179)

Author: liulx20

grape/utils/bitset.h

@@ -25,10 +25,10 @@ limitations under the License.
 #include "thread_pool.h"
 
 #define WORD_SIZE(n) (((n) + 63ul) >> 6)
-#define BYTE_SIZE(n) (((n) + 63ul) >> 3)
+#define BYTE_SIZE(n) (WORD_SIZE(n) * sizeof(uint64_t))
 
 #define WORD_INDEX(i) ((i) >> 6)
-#define BIT_OFFSET(i) ((i) &0x3f)
+#define BIT_OFFSET(i) ((i) & 0x3f)
 
 #define ROUND_UP(i) (((i) + 63ul) & (~63ul))
 #define ROUND_DOWN(i) ((i) & (~63ul))