Fix missing await statement in AsyncDatabase (#119)

src/replit/database/database.py

@@ -77,7 +77,7 @@ async def __aenter__(self) -> "AsyncDatabase":
         return self
 
     async def __aexit__(self, exc_type: Any, exc_value: Any, traceback: Any) -> None:
-        self.sess.close()
+        await self.sess.close()
 
     async def get(self, key: str) -> str:
         """Return the value for key if key is in the database.