Sphinx doesn't render autodoc_docstring_signature correctly (with Python 2?) and pyspark.ml docs are broken

I generated python docs from master locally using `make html`. However, the generated html doc doesn't render class docs correctly. I attached the screenshot from Spark 2.3 docs and master docs generated on my local. Not sure if this is because my local setup.

cc: dongjoon Could you help verify?

The followings are our released doc status. Some recent docs seems to be broken.

2.1.x

(O) https://spark.apache.org/docs/2.1.0/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression
(O) https://spark.apache.org/docs/2.1.1/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression
(X) https://spark.apache.org/docs/2.1.2/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression

2.2.x
(O) https://spark.apache.org/docs/2.2.0/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression
(X) https://spark.apache.org/docs/2.2.1/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression

2.3.x
(O) https://spark.apache.org/docs/2.3.0/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression
(X) https://spark.apache.org/docs/2.3.1/api/python/pyspark.ml.html#pyspark.ml.classification.LogisticRegression