package/lightning: bump version to 2.1.3

package/lightning: bump version to 2.1.3

https://lists.gnu.org/archive/html/lightning/2019-09/msg00033.html
"2.1.3 main features are the new RISC-V port, currently supporting
 only Linux 64 bit"

Build-tested using this defconfig:

BR2_riscv=y
BR2_TOOLCHAIN_BUILDROOT_MUSL=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_PACKAGE_LIGHTNING=y
BR2_PACKAGE_LIGHTNING_DISASSEMBLER=y

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>