fix syntax erroe

extract_01.py

 for x in csv_1_list:
   df = pd.read_csv(os.path.join(target_dir,x), header=0)
   df['frame'] = df['frame'] + FRAME_COUNTER
-  conc_df = pd.concat[conc_df,df]
+  conc_df = pd.concat([conc_df,df])
   FRAME_COUNTER += N_OF_FRAME
 conc_df.to_csv(os.path.join(target_dir,'cam1.csv'), index=False)

extract_02.py

 for x in csv_1_list:
   df = pd.read_csv(os.path.join(target_dir,x), header=0)
   df['frame'] = df['frame'] + FRAME_COUNTER
-  conc_df = pd.concat[conc_df,df]
+  conc_df = pd.concat([conc_df,df])
   FRAME_COUNTER += N_OF_FRAME
 conc_df.to_csv(os.path.join(target_dir,'cam2.csv'), index=False)