Update build.gradle to work with Gradle 5.X
Update build.gradle to work with Gradle 5.X

Running the gradle build script with a recent version of gradle (5.6.3)
required making two changes.

Replace "<<" in task definition with a doLast block, as recommended in
https://docs.gradle.org/current/userguide/upgrading_version_4.html

Remove the "final" keyword from template string definitions. I don't
totally understand why this used to work but now doesn't; the upgrading
document doesn't mention a change to final semantics.

batterseapower/btreemap