[FIX] reqs.txt: bump pillow from 8.0.1 to 8.1.1

Bumps [pillow](https://github.com/python-pillow/Pillow) from 8.0.1 to 8.1.1.
- [Release notes](https://github.com/python-pillow/Pillow/releases)
- [Changelog](https://github.com/python-pillow/Pillow/blob/master/CHANGES.rst)
- [Commits](https://github.com/python-pillow/Pillow/compare/8.0.1...8.1.1

)

Multiple security issues in earlier versions, though generally not
exploitable through Odoo.

Backports are made in Debian/Ubuntu, but for pip users we should bump to
the latest "safe" version.

Courtesy of @dependabot

closes odoo/odoo#68169

Signed-off-by: Christophe Monniez (moc) <moc@odoo.com>

requirements.txt

@@ -30,7 +30,7 @@ ofxparse==0.19
 passlib==1.7.1
 Pillow==5.4.1 ; python_version <= '3.7' and sys_platform != 'win32'
 Pillow==6.1.0 ; python_version <= '3.7' and sys_platform == 'win32'
-Pillow==8.0.1 ; python_version > '3.7'
+Pillow==8.1.1 ; python_version > '3.7'
 polib==1.1.0
 psutil==5.6.6
 psycopg2==2.7.7; sys_platform != 'win32' and python_version < '3.8'