Missing `break` statement from `SimPathsMultiRun.parseCommandLineArgs`

[andrewbaxter439]

"none" will always default to "run" here:

https://github.com/centreformicrosimulation/SimPaths/blob/10abc697321e984bec045d7e4a4f11ead1a98d86/src/main/java/simpaths/experiment/SimPathsMultiRun.java#L212-L225