Fix unit tests with Robolectric 4

app/src/test/java/protect/card_locker/MainActivityTest.java

@@ -32,7 +32,7 @@ import static org.junit.Assert.assertTrue;
 import static org.robolectric.Shadows.shadowOf;
 
 @RunWith(RobolectricTestRunner.class)
-@Config(constants = BuildConfig.class, sdk = 23)
+@Config(sdk = 23)
 public class MainActivityTest
 {
     private SharedPreferences prefs;