[MINOR][DOC] Fix broken word2vec link

Follow-up of [SPARK-12199](https://issues.apache.org/jira/browse/SPARK-12199) and #10193 where a broken link has been left as is.

Author: BenFradet <benjamin.fradet@gmail.com>

Closes #10282 from BenFradet/SPARK-12199.

docs/ml-features.md

@@ -63,7 +63,7 @@ the [IDF Python docs](api/python/pyspark.ml.html#pyspark.ml.feature.IDF) for mor
 `Word2VecModel`. The model maps each word to a unique fixed-size vector. The `Word2VecModel`
 transforms each document into a vector using the average of all words in the document; this vector
 can then be used for as features for prediction, document similarity calculations, etc.
-Please refer to the [MLlib user guide on Word2Vec](mllib-feature-extraction.html#word2Vec) for more
+Please refer to the [MLlib user guide on Word2Vec](mllib-feature-extraction.html#word2vec) for more
 details.
 
 In the following code segment, we start with a set of documents, each of which is represented as a sequence of words. For each document, we transform it into a feature vector. This feature vector could then be passed to a learning algorithm.