Enable parallel configuration caching

According to [Gradle's
documentation](https://docs.gradle.org/current/userguide/configuration_cache.html#config_cache:usage:parallel),
"Configuration cache storing and loading are done sequentially by
default. Parallel storing and loading provide better performance,
however not all builds are compatible with it."  Our build appears to be
compatible, so let's turn this feature on.

That being said, I haven't actually noticed a significant change in
build times.  This feature may affect WALA more in theory than in
practice.

Author: liblit

gradle.properties

@@ -11,6 +11,7 @@ dependency.analysis.print.build.health=true
 
 org.gradle.caching=true
 org.gradle.configuration-cache=true
+org.gradle.configuration-cache.parallel=true
 org.gradle.jvmargs=-XX:MaxMetaspaceSize=512m
 org.gradle.parallel=true