Update from HTTP "async" server from 2.0.1 to 2.1.6

[danielweck]

From:
https://github.com/readium/SDKLauncher-Android/blob/develop/SDKLauncher-Android/libs/androidasync-2.0.1.jar

To:
https://github.com/koush/AndroidAsync

(not sure what the change log is though ...)

[danielweck]

This is fixed in the LCP branch:
https://github.com/readium/SDKLauncher-Android/blob/feature/lcp/SDKLauncher-Android/app/build.gradle#L19

dependencies {
...
    compile 'com.koushikdutta.ion:ion:2.+'
    // compile 'com.koushikdutta.async:androidasync:2.+' ALREADY INCLUDED AS DEPENDENCY OF com.koushikdutta.ion
...
}