Update CONTRIBUTING.md

The build status was still looking for a "master" branch, updated it to point to "main"

.github/workflows/android.yml

@@ -1,9 +1,9 @@
 name: CI_Android
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   Android:
@@ -47,4 +47,4 @@ jobs:
           adb shell find /data/local/tmp/tests -maxdepth 1 -exec chmod +x {} \\\;
 
       - name: Test
-        run: adb shell find /data/local/tmp/tests -name "*_tests" -maxdepth 1 -exec {} \\\;
+        run: adb shell find /data/local/tmp/tests -name "*_tests" -maxdepth 1 -exec {} \\\;

.github/workflows/ios.yml

@@ -1,9 +1,9 @@
 name: CI_iOS
 on:
   push:
-    branches: [ master ]
+    branches: [ main ]
   pull_request:
-    branches: [ master ]
+    branches: [ main ]
 
 jobs:
   iOS:

CONTRIBUTING.md

@@ -17,7 +17,7 @@ Please submit a Contributor License Agreement (CLA) before submitting a pull req
 Your pull request should: 
 
 * Include a description of what your change intends to do
-* Be a child commit of a reasonably recent commit in the **master** branch 
+* Be a child commit of a reasonably recent commit in the **main** branch 
     * Requests need not be a single commit, but should be a linear sequence of commits (i.e. no merge commits in your PR)
 * It is desirable, but not necessary, for the tests to pass at each commit. Please see [README.md](./README.md) for instructions to build the test suite. 
 * Have clear commit messages 

README.md

@@ -1,5 +1,5 @@
 # GSL: Guidelines Support Library
-[![Build Status](https://dev.azure.com/cppstat/GSL/_apis/build/status/microsoft.GSL?branchName=master)](https://dev.azure.com/cppstat/GSL/_build/latest?definitionId=1&branchName=master)
+[![Build Status](https://dev.azure.com/cppstat/GSL/_apis/build/status/microsoft.GSL?branchName=main)](https://dev.azure.com/cppstat/GSL/_build/latest?definitionId=1&branchName=main)
 
 The Guidelines Support Library (GSL) contains functions and types that are suggested for use by the
 [C++ Core Guidelines](https://github.com/isocpp/CppCoreGuidelines) maintained by the [Standard C++ Foundation](https://isocpp.org).

azure-pipelines.yml

@@ -1,5 +1,5 @@
 trigger:
-  - master
+  - main
 
 pr:
   autoCancel: true