MAINTAINERS: Update Ocaml maintainers

Christian has just left Citrix, and Dave almost a decade ago.

Andrii (a XAPI committer) has worked on oxenstored before and has agreed to
step up as a maintainer, and Guillaume wishes to get involved and learn too.
In practice I do a lot of the bindings work, so lets make things official.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Andrii Sultanov <andriy.sultanov@vates.tech>
Acked-by: Guillaume Thouvenin <guillaume.thouvenin@vates.tech>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

MAINTAINERS

@@ -453,8 +453,9 @@ F:	xen/arch/arm/include/asm/linflex-uart.h
 F:	xen/drivers/char/linflex-uart.c
 
 OCAML TOOLS
-M:	Christian Lindig <christian.lindig@citrix.com>
-M:	David Scott <dave@recoil.org>
+M:	Andrew Cooper <andrew.cooper3@citrix.com>
+M:	Andrii Sultanov <andriy.sultanov@vates.tech>
+R:	Guillaume Thouvenin <guillaume.thouvenin@vates.tech>
 S:	Supported
 F:	tools/ocaml/