Removed possible command injection

Author: chieffancypants

lib/printer.js

@@ -93,7 +93,7 @@ function printDirect(parameters){
     }else if (!printer_helper.printDirect){// should be POSIX
         var temp_file_name = path.join(os.tmpDir(),"printing");
         fs.writeFileSync(temp_file_name, data);
-        child_process.exec('lpr -P'+printer+' -oraw -r'+' '+temp_file_name, function(err, stdout, stderr){
+        child_process.execFile('lpr', ['-P' + printer, '-oraw', '-r', temp_file_name], function(err, stdout, stderr){
             if (err !== null) {
                 error('ERROR: ' + err);
                 return;