fix case issue and spaces

Author: yinxusen

examples/src/main/python/ml/polynomial_expansion_example.py

@@ -30,9 +30,9 @@
 
     # $example on$
     df = sqlContext\
-        .createDataFrame([(Vectors.dense([-2.0, 2.3]), ),
-                          (Vectors.dense([0.0, 0.0]), ),
-                          (Vectors.dense([0.6, -1.1]), )],
+        .createDataFrame([(Vectors.dense([-2.0, 2.3]),),
+                          (Vectors.dense([0.0, 0.0]),),
+                          (Vectors.dense([0.6, -1.1]),)],
                          ["features"])
     px = PolynomialExpansion(degree=2, inputCol="features", outputCol="polyFeatures")
     polyDF = px.transform(df)