update buildToolsVersion

[jacintoface]

Can you change several parameters such as buildToolsVersion to read from the configuration file of the project root directory? Now I have encountered a problem with the buildToolsVersion version conflict.

Like this function in build.gradle:
def safeExtGet(prop, fallback) {
rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
}

usage:
compileSdkVersion safeExtGet('compileSdkVersion', 26)
buildToolsVersion safeExtGet('buildToolsVersion', '26.0.2')