move from deprecated ActionBarActivity to AppCompatActivity

src/com/owncloud/android/authentication/AccountAuthenticatorActivity.java

@@ -20,6 +20,7 @@ import android.accounts.AccountAuthenticatorResponse;
 import android.accounts.AccountManager;
 import android.os.Bundle;
 import android.support.v7.app.ActionBarActivity;
+import android.support.v7.app.AppCompatActivity;
 
 /*
  * Base class for implementing an Activity that is used to help implement an AbstractAccountAuthenticator. 
@@ -32,7 +33,7 @@ import android.support.v7.app.ActionBarActivity;
  * then error AccountManager.ERROR_CODE_CANCELED will be called on the response.
  */
 
-public class AccountAuthenticatorActivity extends ActionBarActivity {
+public class AccountAuthenticatorActivity extends AppCompatActivity {
 
     private AccountAuthenticatorResponse mAccountAuthenticatorResponse = null;
     private Bundle mResultBundle = null;