version bump in order to prepare for rodin 3.1 release

de.prob.core/META-INF/MANIFEST.MF

de.prob.eventb.disprover.core/META-INF/MANIFEST.MF

de.prob.eventb.disprover.ui/META-INF/MANIFEST.MF

de.prob.plugin/META-INF/MANIFEST.MF

de.prob.symbolic/META-INF/MANIFEST.MF

de.prob.ui/META-INF/MANIFEST.MF

de.prob.units/META-INF/MANIFEST.MF

de.prob2.disprover.feature/feature.xml

de.prob2.feature/feature.xml

de.prob2.symbolic.feature/feature.xml

de.prob2.units.feature/feature.xml