Updated SMACK to use main branch instead of master

Closes #765

Author: zvonimir

CONTRIBUTING.md

@@ -8,7 +8,7 @@ items before you start contributing:
   By participating, you are expected to honor this code.
 * We use this [git branching
   model](http://nvie.com/posts/a-successful-git-branching-model/). Please avoid
-  working directly on the `master` branch.
+  working directly on the `main` branch.
 * We follow guidelines for [good git commit
   practice](https://wiki.openstack.org/wiki/GitCommitMessages)
 * We follow the [LLVM Coding

README.md

@@ -1,4 +1,4 @@
-[![master branch ci status](https://github.com/smackers/smack/workflows/SMACK%20CI/badge.svg?branch=master)](https://github.com/smackers/smack/actions)
+[![main branch ci status](https://github.com/smackers/smack/workflows/SMACK%20CI/badge.svg?branch=main)](https://github.com/smackers/smack/actions)
 [![develop branch ci status](https://github.com/smackers/smack/workflows/SMACK%20CI/badge.svg?branch=develop)](https://github.com/smackers/smack/actions)
 
 <img src="docs/smack-logo.png" width=400 alt="SMACK Logo" align="right">

docs/installation.md

@@ -51,7 +51,7 @@ the following configurations:
 SMACK's Docker container images can be pulled from Docker Hub directly:
 
 ```shell
-docker pull smackers/smack:stable # built from the master branch
+docker pull smackers/smack:stable # built from the main branch
 docker pull smackers/smack:latest # built from the develop branch
 ```
 
@@ -83,7 +83,7 @@ SMACK depends on the following projects:
 * [Boogie][] or [Corral][] or compatible Boogie-format verifier
 * [sea-dsa][]
 
-See [here](https://github.com/smackers/smack/blob/master/bin/versions) for
+See [here](https://github.com/smackers/smack/blob/main/bin/versions) for
 compatible version numbers of [Boogie][] and [Corral][]. See the appropriate
 installation instructions below for installing these requirements.
 
@@ -198,7 +198,7 @@ shell in the `test` directory by executing
 [Mono]: http://www.mono-project.com/
 [Cygwin]: https://www.cygwin.com
 [.NET]: https://msdn.microsoft.com/en-us/vstudio/aa496123.aspx
-[build.sh]: https://github.com/smackers/smack/blob/master/bin/build.sh
+[build.sh]: https://github.com/smackers/smack/blob/main/bin/build.sh
 [Xcode]: https://developer.apple.com/xcode/
 [Homebrew]: http://brew.sh/
 [Homebrew Cask]: https://formulae.brew.sh/cask/