Fix broken link to POSIX argument conventions

README.md

diff --git a/README.md b/README.md
index 35f97c2..e80277e 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@
 for command-line options][1]. For a more precise description, see the
 "Command-line flag syntax" section below.
 
-[1]: http://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html
+[1]: https://sourceware.org/glibc/manual/latest/html_node/Argument-Syntax.html
 
 pflag is available under the same style of BSD license as the Go language,
 which can be found in the LICENSE file.