Use os.devnull instead of /dev/null

src/filters/rclinfo

@@ -7,7 +7,7 @@ from __future__ import print_function
 
 import rclexecm
 import sys
-import os.path
+import os
 import subprocess
 
 # Prototype for the html document we're returning. Info files are
@@ -55,7 +55,7 @@ class InfoExtractor:
             return False
 
         cmd = b'info --subnodes -o - -f ' + self.file
-        nullstream = open("/dev/null", 'w')
+        nullstream = open(os.devnull, 'w')
         try:
             infostream = subprocess.Popen(cmd, shell=True, bufsize=1,
                                           stderr=nullstream,