Fix a typo in subprocess documentation (GH-25426)
Fix a typo per conversation with vstinner on IRC: in posix => on posix.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index 07b8ad7..b60db58 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -543,7 +543,7 @@
If *cwd* is not ``None``, the function changes the working directory to
*cwd* before executing the child. *cwd* can be a string, bytes or
- :term:`path-like <path-like object>` object. In POSIX, the function
+ :term:`path-like <path-like object>` object. On POSIX, the function
looks for *executable* (or for the first item in *args*) relative to *cwd*
if the executable path is a relative path.