DEVELOPERS: change Vivien Didelot e-mail address

I am exclusively using my Gmail address for now on. Reflect this in
the DEVELOPERS file.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 916497d7d5e2090d99317b0b3982fffa671a831c)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

DEVELOPERS

@@ -2321,7 +2321,7 @@ F:	package/pixz/
 N:	Vinicius Tinti <viniciustinti@gmail.com>
 F:	package/python-thrift/
 
-N:	Vivien Didelot <vivien.didelot@savoirfairelinux.com>
+N:	Vivien Didelot <vivien.didelot@gmail.com>
 F:	board/technologic/ts5500/
 F:	configs/ts5500_defconfig