Fix gradle api usage

[alpha0010]

Currently, local configuration of versions is ignored by this library.

hasProperty() exists on the Project object itself; Project.ext uses has().

You can test by modifying the main app's build.gradle.

buildscript {
    ext {
        buildToolsVersion = "28.0.3"
// [...]

With this mr, setting buildToolsVersion to something older will result in a warning during build. On current master, changes to buildToolsVersion have no effect.

[hyochan]

Oh you are right! Thanks for your kind explanation! 👍