update target sdk to 28

buildscript {

    ext {

        propCompileSdkVersion = 27

        propBuildToolsVersion = "27.0.3"

        propCompileSdkVersion = 28

        propBuildToolsVersion = "28.0.2"

        propMinSdkVersion = 16

        propTargetSdkVersion = propCompileSdkVersion

        propVersionCode = 1

        propVersionName = '4.6.14'

        propVersionName = '4.6.15'

        kotlin_version = '1.2.60'

        support_libs = '27.1.1'

    }