Fix typo in AWSMobileClient (#2841)

From a customer conversation; I'm guessing that this should be `without HostedUI` because the if condition is `if (hostedUIJSON == null)`.

Author: tjleing

aws-android-sdk-mobile-client/src/main/java/com/amazonaws/mobile/client/AWSMobileClient.java

@@ -3271,7 +3271,7 @@ private Runnable _showSignIn(final Activity callingActivity,
                 return new Runnable() {
                     @Override
                     public void run() {
-                        callback.onError(new Exception("showSignIn called with HostedUI options in awsconfiguration.json"));
+                        callback.onError(new Exception("showSignIn called without HostedUI options in awsconfiguration.json"));
                     }
                 };
             }