LookupIn operations raise PathNotFound instead of PathInvalid when a syntactically incorrect path is used

For example,

collection.upsert('test',{:foo=>10, :bar=>{:nested => 11}})

res = collection.lookup_in('test', [LookupInSpec.get('bar..nested')])

res.content(0)

The last line should raise a PathInvalid error, it raises PathNotFound instead

The following failing FIT tests should pass after this is fixed:

• pathInvalidGetLookup
• pathInvalidCountLookup
• pathInvalidExistsLookup