Update refers_to rule regex (#881)

Signed-off-by: Thomas Sedlmayer <tsedlmayer@pmsfit.de>
Co-authored-by: Pierre R. Mai <pmai@pmsf.de>

Author: thomassedlmayer

rules.yml

@@ -5,7 +5,7 @@ is_less_than: '^[ ]\b(is_less_than)\b: ([\s\d]+)$'
 is_equal_to: '^[ ]\b(is_equal_to)\b: ([\s\d]+)$'
 is_different_to: '^[ ]\b(is_different_to)\b: ([\s\d]+)$'
 is_globally_unique: '^[ ]\b(is_globally_unique)\b'
-refers_to: '^[ ]\b(refers_to)\b'
+refers_to: '^[ ]\b(refers_to)\b: ([^,\[\]\s]+|\[\s*(?:[^,\[\]\s]+\s*,\s*)*[^,\[\]\s]+\s*\])$'
 is_iso_country_code: '^[ ]\b(is_iso_country_code)\b'
 first_element: '^[ ]\b(first_element)\b'
 last_element: '^[ ]\b(last_element)\b'