xticks missing for scatter plots with colors
example: https://www.wakari.io/sharing/bundle/adamgreenhall/test-scatter

I think this happens specifically for pandas scatter plots with colorbars in ipython. The xticks are still working for:
- non-colorbar pandas scatter plots
- the same scatter plot using matplotlib
- standard python scripts using `plt.savefig`

related problem with `%matplotlib inline`?: https://github.com/ipython/ipython/issues/1443/
