Fixes the missing of copy ctor for bitset (#154)

Signed-off-by: Tao He <linzhu.ht@alibaba-inc.com>

grape/utils/bitset.h

@@ -25,6 +25,7 @@ limitations under the License.
 #include "thread_pool.h"
 
 #define WORD_SIZE(n) (((n) + 63ul) >> 6)
+#define BYTE_SIZE(n) (((n) + 63ul) >> 3)
 
 #define WORD_INDEX(i) ((i) >> 6)
 #define BIT_OFFSET(i) ((i) &0x3f)
@@ -45,6 +46,12 @@ class Bitset : public Allocator<uint64_t> {
     data_ = this->allocate(size_in_words_);
     clear();
   }
+  Bitset(const Bitset& other)
+      : size_(other.size_),
+        size_in_words_(other.size_in_words_) {
+    data_ = this->allocate(size_in_words_);
+    memcpy(data_, other.data_, BYTE_SIZE(size_));
+  }
   Bitset(Bitset&& other)
       : data_(other.data_),
         size_(other.size_),
@@ -348,6 +355,7 @@ class RefBitset {
 };
 
 #undef WORD_SIZE
+#undef BYTE_SIZE
 #undef WORD_INDEX
 #undef BIT_OFFSET
 #undef ROUND_UP