DEVELOPERS: change Julien Olivain's e-mail address

Julien's e-mail @cotds.org is no longer working:

<juju@cotds.org>: host mail.cotds.org[194.117.244.136] said: 451 4.3.5 Server
    configuration problem (in reply to RCPT TO command)

Use his @free.fr e-mail address instead.

Cc: Julien Olivain <ju.o@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[yann.morin.1998@free.fr: adjust email address after Julien's review]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

DEVELOPERS

@@ -1425,7 +1425,7 @@ F:	board/technologic/ts7680/
 F:	configs/ts7680_defconfig
 F:	package/paho-mqtt-c
 
-N:	Julien Olivain <juju@cotds.org>
+N:	Julien Olivain <ju.o@free.fr>
 F:	board/qmtech/zynq/
 F:	board/technexion/imx8mmpico/
 F:	board/technexion/imx8mpico/