Fix unbounded variable when testing if no_colour is set (embarrassing!)

Author: ralish

script.sh

@@ -63,7 +63,7 @@ function main() {
 
     script_init
     parse_params "$@"
-    if [[ -z $no_colour ]]; then
+    if [[ -z ${no_colour-} ]]; then
         colour_init
     fi
 }

template.sh

@@ -298,7 +298,7 @@ function main() {
 
     script_init
     parse_params "$@"
-    if [[ -z $no_colour ]]; then
+    if [[ -z ${no_colour-} ]]; then
         colour_init
     fi
 }