deps: update doclet version to 1.9.0 (#1054)

Co-authored-by: Jeff Ching <chingor@google.com>

Author: alicejli

pom.xml

@@ -521,7 +521,7 @@
       </activation>
       <properties>
         <!-- default config values -->
-        <docletName>java-docfx-doclet-1.5.0</docletName>
+        <docletName>java-docfx-doclet-1.9.0</docletName>
         <outputpath>${project.build.directory}/docfx-yml</outputpath>
         <projectname>${project.artifactId}</projectname>
         <excludeclasses></excludeclasses>