[Update]Convert into string

dummydatagen.py

@@ -156,5 +156,5 @@ def dummydf():
     #          'Tic-Tac-Toe': 0
     #          }]
     df = pd.read_csv('./assets/uc_result.csv')
-    df['Method']=df['Method'].astype(str)
+    df['Method']=df['Method'].astype("string")
     return df