Fix type error

src/ScanPGunVgrid.py

@@ -143,9 +143,9 @@ def main():
         plt.xlabel('GUN Vgrid (V)')
         plt.ylabel('Booster current (mA)')
         if topup_test_mode == True:
-            ply.ylim(0,0.6)
+            plt.ylim(0,0.6)
         else:
-            ply.ylim(0,1.6)
+            plt.ylim(0,1.6)
         plt.legend(loc=0)
         fig = plt.gcf()
         fig2elog(fig,elog_text)