docs: complete bumping minimal GNU Make version to 3.81

Commit 37d69ee30808 ("docs: bump minimal GNU Make version to 3.81")
changes one entry of GNU make version in the changes.rst, there's still
one more entry saying that one need version 3.80.  Fix that.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
index cef7bc4..e25d63f 100644
--- a/Documentation/process/changes.rst
+++ b/Documentation/process/changes.rst
@@ -70,7 +70,7 @@
 Make
 ----
 
-You will need GNU make 3.80 or later to build the kernel.
+You will need GNU make 3.81 or later to build the kernel.
 
 Binutils
 --------