Bump assertj-core from 3.17.2 to 3.18.0 in /modules/vault (#3384)

Bumps [assertj-core](https://github.com/assertj/assertj-core) from 3.17.2 to 3.18.0.
- [Release notes](https://github.com/assertj/assertj-core/releases)
- [Commits](assertj/assertj@assertj-core-3.17.2...assertj-core-3.18.0)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

modules/vault/build.gradle

@@ -5,6 +5,6 @@ dependencies {
 
     testCompile 'com.bettercloud:vault-java-driver:5.1.0'
     testCompile 'io.rest-assured:rest-assured:4.3.1'
-    testCompile 'org.assertj:assertj-core:3.17.2'
+    testCompile 'org.assertj:assertj-core:3.18.0'
 
 }