fix share chooser dialog design

app/src/main/java/com/keylesspalace/tusky/BaseActivity.java

@@ -16,7 +16,6 @@
 package com.keylesspalace.tusky;
 
 import android.app.ActivityManager;
-import android.app.AlertDialog;
 import android.content.Intent;
 import android.content.SharedPreferences;
 import android.graphics.Bitmap;
@@ -46,6 +45,7 @@ import javax.inject.Inject;
 
 import androidx.annotation.Nullable;
 import androidx.annotation.StringRes;
+import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.app.AppCompatActivity;
 import retrofit2.Call;