Upgrade to dartdoc-0.30.2.

Change-Id: I7e53334582e96590fc738e04fa33a1f4a9a3b4b3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138600
Auto-Submit: Janice Collins <[email protected]>
Reviewed-by: Paul Berry <[email protected]>
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Janice Collins <[email protected]>

Author: jcollins-g

DEPS

@@ -86,7 +86,7 @@ vars = {
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
   "dart_style_tag": "1.3.2",  # Please see the note above before updating.
 
-  "dartdoc_tag" : "v0.30.1",
+  "dartdoc_tag" : "v0.30.2",
   "ffi_tag": "ea88d71b043ee14b268c3aedff14e9eb32e20959",
   "fixnum_tag": "0.10.9",
   "glob_tag": "1.1.7",