message: check project properties to get sdk version
diff: +def safeExtGet(prop, fallback) {
  + rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
  +}
  apply plugin: 'com.android.library'
  android {
  - compileSdkVersion 26
  - buildToolsVersion '26.0.3'
  + compileSdkVersion safeExtGet('compileSdkVersion', 26)
  + buildToolsVersion safeExtGet('compileSdkVersion', '26.0.3')
  defaultConfig {
  consumerProguardFiles 'proguard-rules.pro'
  }
  defaultConfig {
  - minSdkVersion 16
  - targetSdkVersion 26
  + minSdkVersion safeExtGet('minSdkVersion', 16)
  + targetSdkVersion safeExtGet('targetSdkVersion', 26)
  versionCode 1
  versionName "1.0"
  ndk {
  