Bump immutables from 0.9 to 0.14

Bumps [immutables](https://github.com/MagicStack/immutables) from 0.9 to 0.14.
- [Release notes](https://github.com/MagicStack/immutables/releases)
- [Commits](MagicStack/immutables@v0.9...v0.14)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements/base.txt

@@ -29,7 +29,7 @@ flower==0.9.3  # https://github.com/mher/flower
 hiredis==1.0.0
 hyperlink==19.0.0
 idna-ssl==1.1.0
-immutables==0.9
+immutables==0.14
 incremental==17.5.0
 # ERROR: channels-redis 2.4.0 has requirement msgpack~=0.6.0, but you'll have msgpack 1.0.0 which is incompatible.
 msgpack==0.6.0