The baseline image for pygmt/test/test_plot.py:test_plot_matrix is wrong

[maxrjones]

Description of the problem

The current test result is affected by #1313, such that no scaling is applied to the sizes despite the argument incols="0,1,2+s0.005" being included in the test. Since the units are cm and the data values in col 2 of pygmt/tests/data/points.txt are all less than 1, such a scaling would leading to no visible circles being plotted.