modify save location of diff.csv

kpi.py

     #print(norm['stroke_count'].unique())
     #print(norm)
     diff_csv = norm[['frame','diff_diff']]
-    diff_csv.to_csv('./diff.csv')
+    diff_csv.to_csv(os.path.join(file_path, 'diff.csv'))
     #plt.plot(norm['frame'],norm['diff_diff'])
     #plt.savefig('./diff_diff.png')