text: Title: Edges of plot disappear after first loop 
  Body: I am using celluloid to plot a function over 17 years and i love it so far, it works great!
  I have one small problem though, the edges of my plot disappear after the first loop. I have attached images of how this looks. 
  First loop:
  ![wborder](https://user-images.githubusercontent.com/61883982/76109337-8d857900-5fdc-11ea-8ba2-628d6f499982.JPG)
  Second loop:
  ![woborder](https://user-images.githubusercontent.com/61883982/76109357-937b5a00-5fdc-11ea-8b1e-7716d594de59.JPG)
  I am using cartopy and matplotlib in jupyter notebook and this is my code for the animation:
  `
  import matplotlib
  matplotlib.use('Agg')
  from IPython.display import HTML
  from celluloid import Camera
  
  fig=plt.figure(figsize=(9,5))
  cmap=matplotlib.cm.RdBu_r 
  norm=matplotlib.colors.Normalize(vmin=0, vmax=50)
  ax=plt.axes(projection=ccrs.PlateCarree(),extent=[-180, 180, -90, 90])
  ax.set_xticks([-180, -120, -60, 0, 60, 120, 180], crs=ccrs.PlateCarree())
  ax.set_yticks([-90, -60, -30, 0, 30, 60, 90], crs=ccrs.PlateCarree())
  plt.xlabel('Longitude [deg]')
  plt.ylabel('Latitude [deg]')
  
  camera = Camera(fig)
  for i in range(0,(stop-start)+1):
      ax.coastlines()
      plt.scatter(nphi[i], nthe[i], c=mag[i], s=40, norm=norm, cmap=cmap, edgecolor="k")
      ax.text(0, 1.05, 'Global Observatory Plot of SV magnitude from target year ' 
                + str(start+i) + ' in the dB_' + out + '-direction', fontsize=9, transform=ax.transAxes)
      camera.snap()
      
  cbar=plt.colorbar()
  cbar.set_label('Magnitude of SV [nT/yr$^2$]')
  
  animation = camera.animate(interval=800)
  animation.save('Figures/GlobalSVMag.mp4')
  HTML(animation.to_html5_video())
  `
  Is there a way to make the edge appear all the way through the animation?
  