F needs to be in element list.

Otherwise when trying to make a sample molecule
with an F groupAtom, it fails (and crashes
with a segfault)

rmgpy/molecule/atomtype.py

@@ -665,7 +665,7 @@ def getFeatures(self):
 atomTypes['F1s'].setActions(incrementBond=[],               decrementBond=[],               formBond=['F1s'],      breakBond=['F1s'],      incrementRadical=['F1s'], decrementRadical=['F1s'], incrementLonePair=[],      decrementLonePair=[])
 
 #these are ordered on priority of picking if we encounter a more general atomType for make
-allElements=['H', 'C', 'O', 'N', 'S', 'Si', 'Cl', 'Ne', 'Ar', 'He', 'X']
+allElements=['H', 'C', 'O', 'N', 'S', 'Si', 'Cl', 'F', 'Ne', 'Ar', 'He', 'X']
 #list of elements that do not have more specific atomTypes
 nonSpecifics=['H', 'He', 'Ne', 'Ar',]