Correct references to the default branch to use the new name, trunk. (#101)

.github/workflows/pre-commit.yml

@@ -3,7 +3,7 @@ name: pre-commit
 on:
   pull_request:
   push:
-    branches: [master]
+    branches: [trunk]
 
 jobs:
   pre-commit:

.github/workflows/publish-docs.yaml

@@ -2,7 +2,7 @@ name: Publish Carbon Documentation
 on:
   push:
     branches:
-      - master
+      - trunk
 
 jobs:
   build:

CONTRIBUTING.md

@@ -236,7 +236,7 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 ```
 
 For example, see the top of
-[CONTRIBUTING.md](https://github.com/carbon-language/carbon-lang/raw/master/CONTRIBUTING.md)'s
+[CONTRIBUTING.md](https://github.com/carbon-language/carbon-lang/raw/trunk/CONTRIBUTING.md)'s
 raw content.
 
 ### Other files

proposals/template.md

@@ -32,7 +32,7 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 5. Delete this section.
 
 TODOs indicate where content should be updated for a proposal. See
-[Carbon Governance and Evolution](https://github.com/carbon-language/carbon-lang/blob/master/docs/project/evolution.md)
+[Carbon Governance and Evolution](/docs/project/evolution.md)
 for more details.
 
 ## Problem