package/go-bootstrap: bump to version 1.4-bootstrap-20171003

package/go-bootstrap: bump to version 1.4-bootstrap-20171003

See https://golang.org/doc/install/source#bootstrapFromSource

All Go compiler versions > 1.4.x (old) are written in Go, and require a existing
compiled Go version to use to build from source. Buildroot uses a 1.4.x version
in the "go-bootstrap" package to build a C-based Go compiler, and then uses that
compiler to build the main "host-go" compiler.

This commit updates to the latest 1.4.x go-bootstrap branch version recommended
in the documentation, which includes more compatibility fixes.

Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>