README.md: Fix "Docker pid 1 problem" URL

The URL schema of the target site has changed and now returns a 404 for the old URL. This URL accommodates the new URL scheme and points to the original content.

Signed-off-by: Aaron Brooks <aaron@brooks1.net>

Author: abrooks

README.md

@@ -151,7 +151,7 @@ sandbox. You can also change what the value of uid/gid should be in the sandbox.
 IPC namespaces ([CLONE_NEWIPC](https://linux.die.net/man/2/clone)): The sandbox will get its own copy of all the
 different forms of IPCs, like SysV shared memory and semaphores.
 
-PID namespaces ([CLONE_NEWPID](https://linux.die.net/man/2/clone)): The sandbox will not see any processes outside the sandbox. Additionally, bubblewrap will run a trivial pid1 inside your container to handle the requirements of reaping children in the sandbox. This avoids what is known now as the [Docker pid 1 problem](https://blog.phusion.nl/2015/01/20/docker-and-the-pid-1-zombie-reaping-problem/).
+PID namespaces ([CLONE_NEWPID](https://linux.die.net/man/2/clone)): The sandbox will not see any processes outside the sandbox. Additionally, bubblewrap will run a trivial pid1 inside your container to handle the requirements of reaping children in the sandbox. This avoids what is known now as the [Docker pid 1 problem](https://blog.phusion.nl/docker-and-the-pid-1-zombie-reaping-problem/).
 
 
 Network namespaces ([CLONE_NEWNET](https://linux.die.net/man/2/clone)): The sandbox will not see the network. Instead it will have its own network namespace with only a loopback device.