feat(allowed): allow its.sentenceWiseImprotance in doc.out()

Author: sanjayaksaxena

src/allowed.js

@@ -115,7 +115,8 @@ allowed.its4document = new Set( [
   its.negationFlag,
   its.sentiment,
   its.stem,
-  its.readabilityStats
+  its.readabilityStats,
+  its.sentenceWiseImprotance
 ] );