Bump dartdoc to 8e6a95c4aba8def4ef01ccc600b3a3cfb8f3cb9e

Changes:
```
> git log --format="%C(auto) %h %s" e38f392..8e6a95c
 https://dart.googlesource.com/dartdoc.git/+/8e6a95c4 Remove the deprecated nodoc option. (4025)
 https://dart.googlesource.com/dartdoc.git/+/a4a902be Remove the deprecated templates-dir option (4026)
 https://dart.googlesource.com/dartdoc.git/+/37de7494 Bump lints from 5.1.1 to 6.0.0 (4058)
 https://dart.googlesource.com/dartdoc.git/+/56cf68d4 Remove the missing-code-block-language warning (4028)
 https://dart.googlesource.com/dartdoc.git/+/04c27dea Bump to 9.0.0-wip (4057)
 https://dart.googlesource.com/dartdoc.git/+/6fe81c3b Bump to 8.3.4 (4056)
 https://dart.googlesource.com/dartdoc.git/+/5e25cf32 Prepare for automated publishing (4055)
 https://dart.googlesource.com/dartdoc.git/+/6391c68e Don't document elements with `@internal` (4048)
 https://dart.googlesource.com/dartdoc.git/+/2e124adb Remove use of private metadata extension (4053)

```

Diff: https://dart.googlesource.com/dartdoc.git/+/e38f392163a4738a21024acd370d104e0efe72f0..8e6a95c4aba8def4ef01ccc600b3a3cfb8f3cb9e/
Change-Id: I1edc0fa6dbfe3ce4f19d7af89d800315a45abe41
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/431361
Reviewed-by: Samuel Rawlins <[email protected]>
Commit-Queue: Devon Carew <[email protected]>

Author: devoncarew

DEPS

@@ -131,7 +131,7 @@ vars = {
   # EOL comment after a dependency to instead pin at the current revision.
   "ai_rev": "93a9191b6eed79d24fc5d3ec9b514f71c888fc41",
   "core_rev": "635dfa32c261ba078438b74de397f2207904ca78", # https://github.com/dart-lang/core/pull/734
-  "dartdoc_rev": "e38f392163a4738a21024acd370d104e0efe72f0",
+  "dartdoc_rev": "8e6a95c4aba8def4ef01ccc600b3a3cfb8f3cb9e",
   "ecosystem_rev": "815d4ba2e7d11f8695a26f6cbe1262e3b8ff8d0d",
   "flute_rev": "e4ea0459a7debae5e9592c85141707b01fac86c9",
   "http_rev": "e70a41b8b841ada9ba124b3b9e1a4d3c525b8bf9",