UMLR — State::stateInvariant multiplicity too restrictive

The multiplicity of State::stateInvariant is specified as [0..1]. This seems to restrictive, as it common for states to have multiple invariants, especially since this is the most convenient mechanism for specifying the actual values for properties, etc. that define the state. Furthermore, widening the multiplicity to [*] would be in alignment with the multiplicities of pre/postconditions on operations, etc.