Upgrade Gradle & Add Gradle OWASP Dependency-Checks scanner

[jamiejackson]

Adds the ability to do a security scan on the agent's dependencies using:

./gradlew dependencyCheckAnalyze

You may have an alternate way to do this, yourself, but here's an option if you don't have something handy.

I'm submitting this because I'm about to report some vulnerabilities.

[softwareCobbler]

neat, thanks. will bump associated guava deps.