all: rename the "master" branch to "main"

Signed-off-by: Paul Moore <paul@paul-moore.com>
(imported from commit d5ad836)

README.md

@@ -3,8 +3,8 @@
 https://github.com/seccomp/libseccomp
 
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/608/badge)](https://bestpractices.coreinfrastructure.org/projects/608)
-[![Build Status](https://img.shields.io/travis/seccomp/libseccomp/master.svg)](https://travis-ci.org/seccomp/libseccomp)
-[![Coverage Status](https://img.shields.io/coveralls/github/seccomp/libseccomp/master.svg)](https://coveralls.io/github/seccomp/libseccomp?branch=master)
+[![Build Status](https://img.shields.io/travis/seccomp/libseccomp/main.svg)](https://travis-ci.org/seccomp/libseccomp)
+[![Coverage Status](https://img.shields.io/coveralls/github/seccomp/libseccomp/main.svg)](https://coveralls.io/github/seccomp/libseccomp?branch=main)
 [![Language grade: C/C++](https://img.shields.io/lgtm/grade/cpp/g/seccomp/libseccomp.svg?logo=lgtm&logoWidth=18)](https://lgtm.com/projects/g/seccomp/libseccomp/context:cpp)
 
 The libseccomp library provides an easy to use, platform independent, interface