Missing Android supportLibVersion library dependency

Question

I attempted to add an Android library from source as shown in the accepted answer to:

Adding Library Source into Android Studio

I'm getting an error in the build.gradle file:

Error:(4, 0) Could not get unknown property 'supportLibVersion' for object of type org.gradle.api.internal.artifacts.dsl.dependencies.DefaultDependencyHandler.

Here is my build.gradle file:

apply plugin: 'com.android.library'

dependencies {
    compile "com.android.support:support-annotations:${supportLibVersion}"
    compile "com.android.support:support-v4:${supportLibVersion}"
    compile "com.android.support:design:${supportLibVersion}"
    compile rootProject.ext.dep.timber
    compile rootProject.ext.dep.okhttp3
    compile rootProject.ext.dep.lost
...

I can see the library has a file named dependencies.gradle that contains the following:

ext {
    minSdkVersion = 15
    targetSdkVersion = 25
    compileSdkVersion = 25
    buildToolsVersion = "25.0.2"

    versionCode = 11
    versionName = "5.0.0"

    supportLibVersion = "25.2.0"
...

It appears this is where the property is defined, but I think it isn't being seen during the build process. The dependencies.gradle is one level above the build.gradle file, and this may explain why the property isn't seen after I imported the Gradle project. The original library source can be found at:

source library folder

What is the best way to fix this?

Thanks

Mitch