[MINOR][DOC] Update deprecation notes on Python/Hadoop/Scala.

## What changes were proposed in this pull request?

We had better update the deprecation notes about Python 2.6, Hadoop (before 2.6.5) and Scala 2.10 in [2.2.0-RC4](http://people.apache.org/~pwendell/spark-releases/spark-2.2.0-rc4-docs/) documentation. Since this is a doc only update, I think we can update the doc during publishing.

**BEFORE (2.2.0-RC4)**
    ![before](https://cloud.githubusercontent.com/assets/9700541/26799758/aea0dc06-49eb-11e7-8ca3-ed8ce1cc6147.png)

**AFTER**
    ![after](https://cloud.githubusercontent.com/assets/9700541/26799761/b3fef818-49eb-11e7-83c5-334f0e4768ed.png)

## How was this patch tested?

Manual.
```
SKIP_API=1 jekyll build
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #18207 from dongjoon-hyun/minor_doc_deprecation.

docs/index.md

@@ -26,15 +26,13 @@ Spark runs on both Windows and UNIX-like systems (e.g. Linux, Mac OS). It's easy
 locally on one machine --- all you need is to have `java` installed on your system `PATH`,
 or the `JAVA_HOME` environment variable pointing to a Java installation.
 
-Spark runs on Java 8+, Python 2.6+/3.4+ and R 3.1+. For the Scala API, Spark {{site.SPARK_VERSION}}
+Spark runs on Java 8+, Python 2.7+/3.4+ and R 3.1+. For the Scala API, Spark {{site.SPARK_VERSION}}
 uses Scala {{site.SCALA_BINARY_VERSION}}. You will need to use a compatible Scala version
 ({{site.SCALA_BINARY_VERSION}}.x).
 
-Note that support for Java 7 was removed as of Spark 2.2.0.
+Note that support for Java 7, Python 2.6 and old Hadoop versions before 2.6.5 were removed as of Spark 2.2.0.
 
-Note that support for Python 2.6 is deprecated as of Spark 2.0.0, and support for 
-Scala 2.10 and versions of Hadoop before 2.6 are deprecated as of Spark 2.1.0, and may be 
-removed in Spark 2.2.0.
+Note that support for Scala 2.10 is deprecated as of Spark 2.1.0, and may be removed in Spark 2.3.0.
 
 # Running the Examples and Shell