remove build tools version (#639)

Author: dulmandakh

android/build.gradle

@@ -21,7 +21,6 @@ apply plugin: 'com.android.library'
 
 android {
     compileSdkVersion safeExtGet('compileSdkVersion', 28)
-    buildToolsVersion safeExtGet('buildToolsVersion', '28.0.3')
     defaultConfig {
         minSdkVersion safeExtGet('minSdkVersion', 16)
         targetSdkVersion safeExtGet('targetSdkVersion', 26)