Bump assertj-core from 3.15.0 to 3.16.0 in /modules/vault (#2670)

Bumps [assertj-core](https://github.com/joel-costigliola/assertj-core) from 3.15.0 to 3.16.0.
- [Release notes](https://github.com/joel-costigliola/assertj-core/releases)
- [Commits](assertj/assertj@assertj-core-3.15.0...assertj-core-3.16.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

modules/vault/build.gradle

@@ -5,6 +5,6 @@ dependencies {
 
     testCompile 'com.bettercloud:vault-java-driver:5.1.0'
     testCompile 'io.rest-assured:rest-assured:4.3.0'
-    testCompile 'org.assertj:assertj-core:3.15.0'
+    testCompile 'org.assertj:assertj-core:3.16.0'
 
 }