fix orthorhombic typo

[cadenmyers13]

Was directed to this fix from this convo: diffpy/pyobjcryst#53 (comment)

Im not very familiar with C, so please let me know if this is an okay thing to fix like I've done!

[vincefn]

Thanks a lot for this PR !

To be backwards-compatible in C++, the enum will need to use duplicate values for ORTHORHOMBIC and ORTHORHOMBIC.

I think - but I'll need to check- you can declare this using:

enum CrystalSystem
{ TRICLINIC, MONOCLINIC, ORTHORHOMBIC, HEXAGONAL, RHOMBOEDRAL, TETRAGONAL, CUBIC, 
  ORTHOROMBIC=ORTHORHOMBIC // Fix historical typo for backwards compatibility
};

I'll have to test Fox (in a few days) to test the PR.

[cadenmyers13]

@vincefn I made your recommended change. Let me know what you think!