feat: [Android] bump minSDK to 18, targetVersion to 28. Closes #171

Author: reime005

android/build.gradle

@@ -1,24 +1,25 @@
 buildscript {
     repositories {
+        google()
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.3'
+        classpath 'com.android.tools.build:gradle:3.4.1'
     }
 }
 
 apply plugin: 'com.android.library'
 
-def DEFAULT_COMPILE_SDK_VERSION = 27
-def DEFAULT_BUILD_TOOLS_VERSION = "27.0.3"
-def DEFAULT_TARGET_SDK_VERSION = 27
+def DEFAULT_COMPILE_SDK_VERSION = 28
+def DEFAULT_BUILD_TOOLS_VERSION = "28.0.3"
+def DEFAULT_TARGET_SDK_VERSION = 28
 
 android {
     compileSdkVersion project.hasProperty('compileSdkVersion') ? project.compileSdkVersion : DEFAULT_COMPILE_SDK_VERSION
     buildToolsVersion project.hasProperty('buildToolsVersion') ? project.buildToolsVersion : DEFAULT_BUILD_TOOLS_VERSION
 
     defaultConfig {
-        minSdkVersion 16
+        minSdkVersion 18
         targetSdkVersion project.hasProperty('targetSdkVersion') ? project.targetSdkVersion : DEFAULT_TARGET_SDK_VERSION
         versionCode 1
         versionName "1.0"