Update references to master branch

.github/ISSUE_TEMPLATE/BUG_REPORT.md

@@ -16,11 +16,11 @@ about: Something isn't working as expected
 
 Replace this paragraph with a short description of the incorrect incorrect behavior. If this is a regression, please note the last version that the behavior was correct in addition to your current version.
 
-**ArgumentParser version:** `0.1.0` or the `master` branch, for example.
+**ArgumentParser version:** `0.1.0` or the `main` branch, for example.
 **Swift version:** Paste the output of `swift --version` here.
 
 ### Checklist
-- [ ] If possible, I've reproduced the issue using the `master` branch of this package
+- [ ] If possible, I've reproduced the issue using the `main` branch of this package
 - [ ] I've searched for [existing GitHub issues](https://github.com/apple/swift-argument-parser/issues)
 
 ### Steps to Reproduce

CHANGELOG.md

@@ -94,7 +94,7 @@ The 0.2.2 release includes contributions from [interstateone],
 The 0.2.1 release includes contributions from [natecook1000], [NicFontana],
 [schlagelk], [sharplet], and [Wevah]. Thank you!
 
-[comp-guide]: https://github.com/apple/swift-argument-parser/blob/master/Documentation/07%20Completion%20Scripts.md
+[comp-guide]: https://github.com/apple/swift-argument-parser/blob/main/Documentation/07%20Completion%20Scripts.md
 
 ## [0.2.0] - 2020-06-23
 

Documentation/03 Commands and Subcommands.md

@@ -175,4 +175,4 @@ Last but not least, we kick off parsing and execution with a call to the static
 Math.main()
 ```
 
-That's it for this doubly-nested `math` command! This example is also provided as a part of the `swift-argument-parser` repository, so you can see it all together and experiment with it [here](https://github.com/apple/swift-argument-parser/blob/master/Examples/math/main.swift).
+That's it for this doubly-nested `math` command! This example is also provided as a part of the `swift-argument-parser` repository, so you can see it all together and experiment with it [here](https://github.com/apple/swift-argument-parser/blob/main/Examples/math/main.swift).

README.md

@@ -67,7 +67,7 @@ OPTIONS:
   -h, --help              Show help for this command.
 ```
 
-For more information and documentation about all supported options, see [the `Documentation` folder at the root of the repository](https://github.com/apple/swift-argument-parser/tree/master/Documentation).
+For more information and documentation about all supported options, see [the `Documentation` folder at the root of the repository](https://github.com/apple/swift-argument-parser/tree/main/Documentation).
 
 ## Examples