scripts/auto-bootstraps/dobootstrap: fix shellcheck fix

previous fix included some quotes in the output, making no sense and
failing portage down the line

Signed-off-by: Fabian Groffen <[email protected]>

Author: grobian

scripts/auto-bootstraps/dobootstrap

@@ -132,7 +132,7 @@ do_prepare() {
 		USER="${USER}" \
 		CHOST="${chost}" \
 		EPREFIX="${EPREFIX}" \
-		${GENTOO_MIRRORS+GENTOO_MIRRORS=\""${GENTOO_MIRRORS}"\"} \
+		${GENTOO_MIRRORS+GENTOO_MIRRORS="${GENTOO_MIRRORS}"} \
 		${DOLOCAL+DOLOCAL=1} \
 		${RESUME+RESUME=1} \
 		${LATEST_TREE_YES+LATEST_TREE_YES=1} \