changed to openapi-generator plugin version 5.1.1 and some minor fixes

Author: danielkocot

build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id 'org.springframework.boot' version '2.3.5.RELEASE'
     id 'io.spring.dependency-management' version '1.0.10.RELEASE'
-    id 'org.openapi.generator' version '4.3.1'
+    id 'org.openapi.generator' version '5.1.1'
     id 'de.undercouch.download' version '4.1.1'
     id 'org.asciidoctor.convert' version '1.5.8'
     id 'org.jetbrains.gradle.plugin.idea-ext' version '0.5'
@@ -38,7 +38,7 @@ dependencies {
     implementation 'io.springfox:springfox-boot-starter:3.0.0'
 
     compile 'io.springfox:springfox-swagger-ui:3.0.0'
-    //needed for swagger code generation
+    //needed for OpenAPI code generation
     compile "io.springfox:springfox-swagger2:3.0.0"
     compile "org.openapitools:jackson-databind-nullable:0.1.0"