#21347: use string not list in shell=True example.

Patch by Akira.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index ce3097b..854993c 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -1013,7 +1013,7 @@
 
    (child_stdout, child_stdin) = popen2.popen2("somestring", bufsize, mode)
    ==>
-   p = Popen(["somestring"], shell=True, bufsize=bufsize,
+   p = Popen("somestring", shell=True, bufsize=bufsize,
              stdin=PIPE, stdout=PIPE, close_fds=True)
    (child_stdout, child_stdin) = (p.stdout, p.stdin)