add axes3d to figure (AtsushiSakai#766)

Author: zlingkang

Bipedal/bipedal_planner/bipedal_planner.py

@@ -51,6 +51,7 @@ def walk(self, t_sup=0.8, z_c=0.8, a=10, b=1, plot=False):
         if plot:
             fig = plt.figure()
             ax = Axes3D(fig)
+            fig.add_axes(ax)
             com_trajectory_for_plot = []
 
         px, py = 0.0, 0.0  # reference footstep position