Fix spelling error in man page, no functional changes.

doc/obfs4proxy.1

@@ -35,7 +35,7 @@ Disable the IP address scrubber when logging, storing personally identifiable
 information in the logs.
 .TP
 \fB\-\-obfs4\-distBias\fR
-When generating probability distributions for the obfs4 lenght and timing
+When generating probability distributions for the obfs4 length and timing
 obfuscation, generate biased distributions similar to ScrambleSuit.
 .SH ENVIORNMENT
 obfs4proxy honors all of the enviornment variables as specified in the Tor