fix: bump compile sdk version to 28 (#33)

Author: Naturalclar

android/build.gradle

@@ -12,12 +12,12 @@ buildscript {
 apply plugin: 'com.android.library'
 
 android {
-    compileSdkVersion 23
+    compileSdkVersion 28
     buildToolsVersion "28.0.3"
 
     defaultConfig {
         minSdkVersion 16
-        targetSdkVersion 22
+        targetSdkVersion 28
         versionCode 1
         versionName "1.0"
     }