Bump io.vertx:vertx-docgen from 0.9.4 to 3.5.1

Bumps io.vertx:vertx-docgen from 0.9.4 to 3.5.1.

---
updated-dependencies:
- dependency-name: io.vertx:vertx-docgen
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

pom.xml

@@ -50,7 +50,7 @@
       <dependency>
         <groupId>io.vertx</groupId>
         <artifactId>vertx-docgen</artifactId>
-        <version>0.9.4</version>
+        <version>3.5.1</version>
       </dependency>
       <dependency>
         <groupId>org.scala-lang</groupId>