Standardize on 'main' as branch name

Author: jonhoo

github/workflows/coverage.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: coverage
 jobs:

github/workflows/features.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: cargo hack
 jobs:

github/workflows/minimal.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: With dependencies at minimal versions
 jobs:

github/workflows/msrv.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: Minimum Supported Rust Version
 jobs:

github/workflows/os-check.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: os check
 jobs:

github/workflows/test.yml

@@ -1,6 +1,6 @@
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
 name: cargo test
 jobs: