ContextSpellChecker: fix unpredictable behavior of mutable.HashMap modification

genVocab would not iterate over all vocab in the mutable.HashMap. This is due to
the iterator state of the mutable.HashMap being changed during iteration. Fixed by
using mapValuesInPlace.

Author: DevinTDHa

src/main/scala/com/johnsnowlabs/nlp/annotators/spell/context/ContextSpellCheckerApproach.scala

@@ -621,9 +621,7 @@ class ContextSpellCheckerApproach(override val uid: String)
 
     // compute frequencies - logarithmic
     totalCount = math.log(totalCount)
-    for (key <- vocab.keys) {
-      vocab.update(key, math.log(vocab(key)) - totalCount)
-    }
+    vocab.mapValuesInPlace { case (_, v) => math.log(v) - totalCount }
     logger.info(s"Vocabulary size: ${vocab.size}")
     (vocab, classes)
   }