[MINOR] Fix Typos 'a -> an'

## What changes were proposed in this pull request?

`a` -> `an`

I use regex to generate potential error lines:
`grep -in ' a [aeiou]' mllib/src/main/scala/org/apache/spark/ml/*/*scala`
and review them line by line.

## How was this patch tested?

local build
`lint-java` checking

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #13317 from zhengruifeng/a_an.

1 files changed, 3 insertions, 3 deletions

diff --git a/python/pyspark/mllib/regression.py b/python/pyspark/mllib/regression.py
index 43d9072a24..705022934e 100644
--- a/python/pyspark/mllib/regression.py
+++ b/python/pyspark/mllib/regression.py
@@ -648,7 +648,7 @@ class IsotonicRegressionModel(Saveable, Loader):
 
     @since("1.4.0")
     def save(self, sc, path):
-        """Save a IsotonicRegressionModel."""
+        """Save an IsotonicRegressionModel."""
         java_boundaries = _py2java(sc, self.boundaries.tolist())
         java_predictions = _py2java(sc, self.predictions.tolist())
         java_model = sc._jvm.org.apache.spark.mllib.regression.IsotonicRegressionModel(
@@ -658,7 +658,7 @@ class IsotonicRegressionModel(Saveable, Loader):
     @classmethod
     @since("1.4.0")
     def load(cls, sc, path):
-        """Load a IsotonicRegressionModel."""
+        """Load an IsotonicRegressionModel."""
         java_model = sc._jvm.org.apache.spark.mllib.regression.IsotonicRegressionModel.load(
             sc._jsc.sc(), path)
         py_boundaries = _java2py(sc, java_model.boundaryVector()).toArray()
@@ -694,7 +694,7 @@ class IsotonicRegression(object):
     @since("1.4.0")
     def train(cls, data, isotonic=True):
         """
-        Train a isotonic regression model on the given data.
+        Train an isotonic regression model on the given data.
 
         :param data:
           RDD of (label, feature, weight) tuples.