[Docs] fix minor MLlib case typo

Also make the list of features consistent in style.

Author: nchammas

README.md

@@ -4,8 +4,8 @@ Spark is a fast and general cluster computing system for Big Data. It provides
 high-level APIs in Scala, Java, and Python, and an optimized engine that
 supports general computation graphs for data analysis. It also supports a
 rich set of higher-level tools including Spark SQL for SQL and structured
-data processing, MLLib for machine learning, GraphX for graph processing,
-and Spark Streaming.
+data processing, MLlib for machine learning, GraphX for graph processing,
+and Spark Streaming for stream processing.
 
 <http://spark.apache.org/>