Fix the 0.57 version packaging problem

Author: 2534290808

android/build.gradle

@@ -1,12 +1,16 @@
 apply plugin: 'com.android.library'
 
+def safeExtGet(prop, fallback) {
+    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+}
+
 android {
-    compileSdkVersion 25
-    buildToolsVersion "25.0.2"
+    compileSdkVersion safeExtGet("compileSdkVersion",25)
+    buildToolsVersion safeExtGet("buildToolsVersion","25.0.2")
 
     defaultConfig {
-        minSdkVersion 16
-        targetSdkVersion 26
+        minSdkVersion safeExtGet('minSdkVersion', 16)
+        targetSdkVersion safeExtGet('targetSdkVersion', 26)
         versionCode 1
         versionName "1.0"