making wireguard work on RHEL7/etc.

[wireguard at wut.to]

another fix for RHEL7/etc., the version of bash included doesn't support
'local -n' (neither does Amazon AMI Linux either)

diff --git a/src/tools/wg-quick.bash b/src/tools/wg-quick.bash
index 6edcd3a..afec996 100755
--- a/src/tools/wg-quick.bash
+++ b/src/tools/wg-quick.bash
@@ -54,7 +54,7 @@ parse_options() {
 }

 read_bool() {
-       local -n out="$1"
+       local out="$1"
        case "$2" in
        true) out=1 ;;
        false) out=0 ;;