Fix UnknownHostException in OkHttpNetworkHandler

03-03 09:12:33.444 I/MonoDroid( 2255): UNHANDLED EXCEPTION: Java.Net.UnknownHostException: Exception of type 'Java.Net.UnknownHostException' was thrown.
03-03 09:12:33.444 I/MonoDroid( 2255):   at Android.Runtime.JNIEnv.CallIntMethod (IntPtr jobject, IntPtr jmethod) [0x00063] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.10.2-branch/e0ba8107/source/monodroid/src/Mono.Android/src/Runtime/JNIEnv.g.cs:350 
03-03 09:12:33.444 I/MonoDroid( 2255):   at Java.Net.HttpURLConnection.get_ResponseCode () [0x00043] in /Users/builder/data/lanes/monodroid-mlion-monodroid-4.10.2-branch/e0ba8107/source/monodroid/src/Mono.Android/platforms/android-14/src/generated/Java.Net.HttpURLConnection.cs:499 
03-03 09:12:33.444 I/MonoDroid( 2255):   at ModernHttpClient.OkHttpNetworkHandler+<SendAsync>c__async0+<SendAsync>c__AnonStorey9.<>m__1 () [0x00019] in /Users/paul/code/paulcbetts/ModernHttpClient/src/ModernHttpClient.Android/OkHttpNetworkHandler.cs:52 
03-03 09:12:33.444 I/MonoDroid( 2255):   at System.Threading.Tasks.TaskActionInvoker+FuncInvoke`1[System.Net.Http.HttpResponseMessage].Invoke (System.Threading.Tasks.Task owner, System.Object state, System.Threading.Tasks.Task context) [0x00000] in <filename unknown>:0 
03-03 09:12:33.444 I/MonoDroid( 2255):   at System.Threading.Tasks.Task.InnerInvoke () [0x00000] in <filename unknown>:0 
03-03 09:12:33.444 I/MonoDroid( 2255):   at System.Threading.Tasks.Task.ThreadStart () [0x00000] in <filename unknown>:0 
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