electrum: 3.0.2 -> 3.0.3

Note that due to runtime impurities, non-NixOS users must prepend and export
QT_PLUGIN_PATH=${qt5.qtbase.qtPluginPrefix}
and
LD_LIBRARY_PATH=/run/opengl-driver/lib
before running electrum, lest it fail to find runtime dependencies or pick
up mismatching libraries from the host system.