Update compile and target sdk version.

app/build.gradle

@@ -9,8 +9,8 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 25
-    buildToolsVersion '25.0.2'
+    compileSdkVersion 27
+    buildToolsVersion '27.0.1'
 
     defaultConfig {
         applicationId "com.etesync.syncadapter"

app/src/main/java/com/etesync/syncadapter/App.java

@@ -31,9 +31,9 @@ import android.provider.CalendarContract;
 import android.provider.ContactsContract;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.support.v4.app.NotificationCompat;
 import android.support.v4.app.NotificationManagerCompat;
 import android.support.v4.content.ContextCompat;
-import android.support.v7.app.NotificationCompat;
 import android.util.Log;
 
 import com.etesync.syncadapter.log.LogcatHandler;

app/src/main/java/com/etesync/syncadapter/NotificationHelper.java

@@ -7,8 +7,8 @@ import android.content.Intent;
 import android.database.sqlite.SQLiteException;
 import android.net.Uri;
 import android.os.Bundle;
+import android.support.v4.app.NotificationCompat;
 import android.support.v4.app.NotificationManagerCompat;
-import android.support.v7.app.NotificationCompat;
 
 import com.etesync.syncadapter.journalmanager.Exceptions;
 import com.etesync.syncadapter.ui.AccountSettingsActivity;