Fixed tr construct reporting a warning (Closes: #452669).

ChangeLog

@@ -3,6 +3,7 @@ version 0.9.6 -- unreleased
 	 . fix bug in cstream definition, thanks Jamie McClelland
 	 . Allow the entire backup run to be halted by an action, thanks to
 	   Matthew Palmer (Closes: #455836)
+	 . Fixed tr construct reporting a warning (Closes: #452669)
     handler changes
 	dup:
 	 . General cleanup

src/backupninja.in

@@ -180,7 +180,7 @@ function check_perms() {
 
 # simple lowercase function
 function tolower() {
-	echo "$1" | tr [:upper:] [:lower:]
+	echo "$1" | tr '[:upper:]' '[:lower:]'
 }
 
 # simple to integer function