title: OkHttp support for SDK versions less than 21
body: <p>OkHttp has <a href="https://medium.com/square-corner-blog/okhttp-3-13-requires-android-5-818bb78d07ce" rel="nofollow noreferrer">recently dropped support for Android 4</a>, except via a <a href="https://github.com/square/okhttp/tree/okhttp_3.12.x" rel="nofollow noreferrer">separate <code>3.12.x</code> branch</a> that will be supported until end of Dec 2021 (and probably receive no more than critical updates or bugfixes).</p>
  
  <p>On the assumption that you wish to continue to support Android 4, like I do, since 10% of the Android user base is still a significant proportion, and don't want to be stuck in a dead-end branch...</p>
  
  <p>Rather than being stuck on the <code>3.12.x</code> branch for all sdk versions, is there any way of using the <code>3.12</code> branch for <code>sdk &lt; 21</code> and the <code>3.13</code> branch for <code>sdk &gt;= 21</code>, a bit like it would of course be possible to use <code>HttpUrlConnection</code> for <code>sdk &lt; 21</code> and OkHttp <code>3.13</code> for <code>sdk &gt;= 21</code>?</p>