package/go-bootstrap: bump version to 1.4.3

package/go-bootstrap: bump version to 1.4.3

This bump includes
https://go.googlesource.com/go/+/a527bdbda39c48fa772d8d54eb6b849f240442c1

which fixes a gcc6-related compile error

cmd/6c
/home/buildroot/br2/output/build/host-go-bootstrap-1.4.2/src/cmd/6c/txt.c: In function 'gmove':
/home/buildroot/br2/output/build/host-go-bootstrap-1.4.2/src/cmd/6c/txt.c:995:28: error: left shift of negative value [-Werror=shift-negative-value]
     f->vconst |= (vlong)~0 << 32;
                            ^~
/home/buildroot/br2/output/build/host-go-bootstrap-1.4.2/src/cmd/6c/txt.c:1045:28: error: left shift of negative value [-Werror=shift-negative-value]
     f->vconst |= (vlong)~0 << 32;
                            ^~
cc1: all warnings being treated as errors

not yet caught by autobuilders using this defconfig:

http://autobuild.buildroot.net/results/394/394e22be0ef986463e97b3040dad8f978262732c/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>