fix plot issue in random_inverse_kinematics.py (#1007)

Author: AtsushiSakai

ArmNavigation/n_joint_arm_3d/NLinkArm3d.py

@@ -127,7 +127,8 @@ def inverse_kinematics(self, ref_ee_pose, plot=False):
 
         if plot:
             self.fig = plt.figure()
-            self.ax = Axes3D(self.fig)
+            self.ax = Axes3D(self.fig, auto_add_to_figure=False)
+            self.fig.add_axes(self.ax)
 
             x_list = []
             y_list = []