Incorrect license detection

This, see in https://github.com/foundation/foundation-sites/tree/v6.4.1:
```
/**
* Foundation for Sites by ZURB
* Version 6.4.1
* foundation.zurb.com
* Licensed under MIT Open Source
*/
/*! normalize-scss | MIT/GPLv2 License | bit.ly/normalize-scss */
```

This is reported as two matches of `mit` AND another of `gpl-2.0`
```
license_detections:
- license_expression: mit AND gpl-2.0
detection_log:
- not-combined
matches:
- score: '100.0'
start_line: 5
end_line: 5
matched_length: 3
match_coverage: '100.0'
matcher: 2-aho
license_expression: mit
rule_identifier: mit_172.RULE
rule_url: https://github.com/nexB/scancode-toolkit/tree/develop/src/licensedcode/data/rules/mit_172.RULE
matched_text: Licensed under MIT
- score: '100.0'
start_line: 7
end_line: 7
matched_length: 2
match_coverage: '100.0'
matcher: 2-aho
license_expression: gpl-2.0
rule_identifier: gpl-2.0_818.RULE
rule_url: https://github.com/nexB/scancode-toolkit/tree/develop/src/licensedcode/data/rules/gpl-2.0_818.RULE
matched_text: GPLv2 License |
```
but we should have instead detected `mit` AND `mit OR gpl-2.0` and reported a top level expression of `mit OR gpl-2.0`