py3: pass str in os.sysconf()

os.sysconf() doesn't accepts bytes on Python 3. Adding r'' will make
sure b'' is not added here.

mercurial/worker.py

@@ -26,7 +26,7 b' def countcpus():'
 
     # posix
     try:
-        n = int(os.sysconf('SC_NPROCESSORS_ONLN'))
+        n = int(os.sysconf(r'SC_NPROCESSORS_ONLN'))
         if n > 0:
             return n
     except (AttributeError, ValueError):