[mustache_template] Fix broken README link (#11306)

pub.dev flagged this link since it used http rather than https, but it
turns out it's also no longer a valid link; that domain doesn't resolve.
This updates to the correct domain, and to a secure link.

Part of flutter/flutter#183844

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[repository CHANGELOG style]:
https://github.com/flutter/flutter/blob/master/docs/ecosystem/contributing/README.md#changelog-style
[test exemption]:
https://github.com/flutter/flutter/blob/master/docs/contributing/Tree-hygiene.md#tests

Author: stuartmorgan-g

third_party/packages/mustache_template/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.0.4
+
+* Fixes a broken README link to the Mustache manual.
+
 ## 2.0.3
 
 * Updates minimum supported SDK version to Flutter 3.35/Dart 3.9.

third_party/packages/mustache_template/README.md

@@ -2,7 +2,7 @@
 
 A Dart library to parse and render [mustache templates](https://mustache.github.io/).
 
-See the [mustache manual](http://mustache.github.com/mustache.5.html) for detailed usage information.
+See the [mustache manual](https://mustache.github.io/mustache.5.html) for detailed usage information.
 
 This library passes all [mustache specification](https://github.com/mustache/spec/tree/master/specs) tests.
 

third_party/packages/mustache_template/pubspec.yaml

@@ -2,7 +2,7 @@ name: mustache_template
 description: A templating library that implements the Mustache template specification
 repository: https://github.com/flutter/packages/tree/main/third_party/packages/mustache_template
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+mustache_template%22
-version: 2.0.3
+version: 2.0.4
 
 environment:
   sdk: ^3.9.0