fix some small bug in clear

vector/src/vector.hpp

@@ -360,14 +360,14 @@ class vector {
   void clear() {
     if (raw_beg != nullptr) {
       for (size_t i = 0; i < current_length; ++i) {
-        alloc.destroy(raw_beg + i);
+        std::allocator_traits<decltype(alloc)>::destroy(alloc, raw_beg + i);
       }
-      current_length = 0;
       alloc.deallocate(raw_beg, allocated_length);
     }
     raw_beg = alloc.allocate(1);
     raw_end = raw_beg;
     allocated_length = 1;
+    current_length = 0;
   }
   /**
    * inserts value before pos