Update README.markdown

In my machine I got installed following packages:

`cat  ~/.m2/repository/android/android/maven-metadata-local.xml`

    <?xml version="1.0" encoding="UTF-8"?>
    <metadata>
      <groupId>android</groupId>
      <artifactId>android</artifactId>
      <versioning>
        <release>4.2.2_r2</release>
        <versions>
          <version>1.5_r4</version>
          <version>1.6_r3</version>
          <version>2.1_r3</version>
          <version>2.2_r3</version>
          <version>2.3.3_r2</version>
          <version>3.0_r2</version>
          <version>3.1_r3</version>
          <version>3.2_r1</version>
          <version>4.0_r3</version>
          <version>4.0.3_r3</version>
          <version>4.1.2_r4</version>
          <version>4.2.2_r2</version>
        </versions>
        <lastUpdated>20130618152101</lastUpdated>
      </versioning>
    </metadata>

So I'd recommend to use `4.2.2_r2` instead of `4.2_r2`