Don't suggest a comma between "rather than"

Fixes https://languagetool.org/regression-tests/20140427/result_en_20140427.html

```
+Line 1, column 1, Rule ID: SENT_START_CONJUNCTIVE_LINKING_ADVERB_COMMA[1]
+Message: Did you forgot a ',' after a conjunctive/linking adverb?
+Suggestion: ,
+Rather than focus on formal causes, as Aristotle did, Th...
+^^^^^^                                                  
+
+Title: Aristotle
```