update gradle config

app/build.gradle

@@ -1,13 +1,12 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 25
-    buildToolsVersion '27.0.3'
+    compileSdkVersion 28
 
     defaultConfig {
         applicationId "com.example.app"
         minSdkVersion 21
-        targetSdkVersion 25
+        targetSdkVersion 28
         versionCode 1
         versionName "1.0"
     }