Upgrade to AssertJ 3.11.1

Author: wilkinsona

build.gradle

@@ -82,7 +82,7 @@ subprojects {
 			dependency 'junit:junit:4.12'
 			dependency 'io.rest-assured:rest-assured:3.0.7'
 			dependency 'org.apache.pdfbox:pdfbox:2.0.7'
-			dependency 'org.assertj:assertj-core:2.9.1'
+			dependency 'org.assertj:assertj-core:3.11.1'
 			dependency 'org.asciidoctor:asciidoctorj-pdf:1.5.0-alpha.18'
 			dependency 'org.hamcrest:hamcrest-core:1.3'
 			dependency 'org.hamcrest:hamcrest-library:1.3'