Correct build errors

sample/build.gradle

@@ -3,13 +3,12 @@ apply plugin: 'kotlin-android'
 apply plugin: 'kotlin-android-extensions'
 
 android {
-    compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
+
+    compileSdkVersion 28
 
     defaultConfig {
         applicationId "com.github.aachartmodel.aainfographics.demo"
-        minSdkVersion rootProject.ext.minSdkVersion
-        targetSdkVersion rootProject.ext.targetSdkVersion
+        minSdkVersion 19
         versionCode 1
         versionName "1.0.0"
     }