Small fix.

Use function instead of original expression.

db/skiplist.h

@@ -243,7 +243,7 @@ int SkipList::RandomHeight() {
   // Increase height with probability 1 in kBranching
   static const unsigned int kBranching = 4;
   int height = 1;
-  while (height < kMaxHeight && ((rnd_.Next() % kBranching) == 0)) {
+  while (height < kMaxHeight && rnd_.OneIn(kBranching)) {
     height++;
   }
   assert(height > 0);