build errors due to support library inconsistencies

[contriteobserver]

support libraries are inconsistent, gradle.properties set supportLibraryVersion=25.4.0 while sample/build.gradle depends upon api 'com.android.support:appcompat-v7:27.0.2'

so a command line of ANDROID_SDK_ROOT=~/Android/Sdk/ ./gradlew clean assemble results in errors like:

AAPT: error: resource android:attr/colorError not found.
AAPT: error: resource android:attr/colorError not found.
AAPT: error: style attribute 'android:attr/keyboardNavigationCluster' not found.
AAPT error resource android attr/font not found
AAPT error resource android attr/fontStyle not found
AAPT error resource android attr/fontWeight not found