ci: add macOS 11 Big Sur

Remove all traces of Travis CI

Change-Id: I1839ae96e41678f722cba052a56ae7c54255defd
diff --git a/docs/INSTALL.rst b/docs/INSTALL.rst
index 64a4239..7c90deb 100644
--- a/docs/INSTALL.rst
+++ b/docs/INSTALL.rst
@@ -11,6 +11,7 @@
 -  Ubuntu 20.04 (amd64)
 -  Ubuntu 21.04 (amd64)
 -  macOS 10.15
+-  macOS 11 (Intel only)
 -  CentOS 8
 
 ndn-cxx is known to work on the following platforms, although they are not officially
@@ -24,7 +25,6 @@
 -  FreeBSD >= 11.3
 -  macOS 10.13
 -  macOS 10.14
--  macOS 11 (Intel only)
 
 Prerequisites
 -------------