Don't hardcode errno constant

The value of ENOENT is architecture-dependent, so don't assume it's
always 2.

youtube_dl/YoutubeDL.py

@@ -326,7 +326,7 @@ class YoutubeDL(object):
                         ['fribidi', '-c', 'UTF-8'] + width_args, **sp_kwargs)
                 self._output_channel = os.fdopen(master, 'rb')
             except OSError as ose:
-                if ose.errno == 2:
+                if ose.errno == errno.ENOENT:
                     self.report_warning('Could not find fribidi executable, ignoring --bidi-workaround . Make sure that  fribidi  is an executable file in one of the directories in your $PATH.')
                 else:
                     raise