Move to setting maven version via SupporLibrary extension.

Test: ./gradlew createArchive
Change-Id: Ifa145712bc3b68ef561d8d7f9e21e97c79b705d1
diff --git a/customtabs/build.gradle b/customtabs/build.gradle
index ade1bda..28b5f99 100644
--- a/customtabs/build.gradle
+++ b/customtabs/build.gradle
@@ -1,4 +1,5 @@
 import android.support.LibraryGroups
+import android.support.LibraryVersions
 
 plugins {
     id("SupportAndroidLibraryPlugin")
@@ -26,6 +27,7 @@
 supportLibrary {
     name = "Android Support Custom Tabs"
     publish = true
+    mavenVersion = LibraryVersions.SUPPORT_LIBRARY
     mavenGroup = LibraryGroups.SUPPORT
     inceptionYear = "2015"
     description = "Android Support Custom Tabs"