fix(intrinsics): change Fn::Sub to allow AWS pseudo parameters

Adds `:` character to regex for variable match, allowing all AWS pseudo parameters to be replaced

fixes awslabs#274, awslabs#202

intrinsics/fnsub.go

@@ -36,7 +36,7 @@ func FnSub(name string, input interface{}, template interface{}) interface{} {
 
 	case string:
 		// Look up references for each of the variables
-		regex := regexp.MustCompile(`\$\{([\.0-9A-Za-z]+)\}`)
+		regex := regexp.MustCompile(`\$\{([\.:0-9A-Za-z]+)\}`)
 		variables := regex.FindAllStringSubmatch(val, -1)
 		for _, variable := range variables {