Fix UnnecessaryParentReference handling of concatenated `&`

Fix issue where the linter would report an incorrect lint for code like
the following:

    & + &:hover {
      ...
    }

Change-Id: Iac35b0e68265f5c029b8d28f0685bba24c1d0df8
Reviewed-on: http://gerrit.causes.com/43355
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Cut version 0.29.0

Change-Id: Iffd3a391dbe2b34f17afa772bdb5b9a42f2ca70d
Reviewed-on: http://gerrit.causes.com/43356
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>
Merge remote-tracking branch 'upstream/master'
Improving VendorPrefixes linter