Fix HtmlRenderer code example in documentation (#10790)

documentation/components/components-grid.asciidoc

@@ -504,7 +504,7 @@ Set the renderer in the [classname]#Grid.Column# object:
 +
 [source, java]
 ----
-Column<Person, String> htmlColumn grid.addColumn(person ->
+Column<Person, String> htmlColumn = grid.addColumn(person ->
       "<a href='" + person.getDetailsUrl() + "' target='_top'>info</a>",
       new HtmlRenderer());
 ----