Update to 5.1.0-rc2
    
    This release brings in many new features:
    
    1) KiCad now uses gtk3 rather than gtk2
    2) The ngspice simulator is now supported
    3) python3 is used instead of python2, which allows us to support
       scripting.
    
    Note that in some cases, graphics artifacts may be seen at certain zoom
    levels.  If you are bothered by this, switch to "Fallback graphics"
    (rather than Accelerated graphics), and also select "High Quality
    Antialiasing" for the Fallback graphics.  This will eliminate the
    artifacts.