Fix unaesthetic indentation

The current documentation build looks like this:

$ make htmldocs
SPHINX htmldocs --> file:///home/willy/kernel/linux-next/Documentation/output
make[2]: Nothing to be done for 'html'.
WARNING: The kernel documentation build process
support for Sphinx v3.0 and above is brand new. Be prepared for
possible issues in the generated output.
$

That extra indentation before my next prompt isn't pretty. This patch
fixes it, but I'm not a pythonista, and maybe there's a better way.

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
[jc: tweaked for the "better way"]
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/conf.py

···
 if major >= 3:
     sys.stderr.write('''WARNING: The kernel documentation build process
         support for Sphinx v3.0 and above is brand new. Be prepared for
-        possible issues in the generated output.
-        ''')
+        possible issues in the generated output.\n''')
     if (major > 3) or (minor > 0 or patch >= 2):
         # Sphinx c function parser is more pedantic with regards to type
         # checking. Due to that, having macros at c:function cause problems.