scripts: use go get with full path

scripts/update.sh

@@ -31,7 +31,7 @@ find_or_install() {
             echo "Installing ${url}" >&2
             # Go needs to be installed.
             is_installed go || die "Go needs to be installed. See https://golang.org/dl/"
-            go get -u -d ${url} >&2 || true
+            go get -u -d ${url}/${relpath} >&2 || true
             go install ${url}/${relpath} \
                 || die "Could not install ${bin}"
         fi