scale issue of Plotter2D

[HMX2013]

Thanks for your great work, when using the the jsk rviz plugins in ubutnu or vmware, I found that if the scale value of the display is not 100%, It may have the following problem. I don't see any option to change the font size of this value in Plotter2D. This problem puzzle me, hope it can be solve on day.

[mqcmd196]

@HMX2013 Please try https://github.com/jsk-ros-pkg/jsk_visualization/pull/878