doc: Fix spelling of 'Transmission'

Signed-off-by: Sebastian Ramacher <sramacher@debian.org>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

doc/protocols.texi

@@ -638,7 +638,7 @@ avplay sap://[ff0e::2:7ffe]
 
 @section tcp
 
-Trasmission Control Protocol.
+Transmission Control Protocol.
 
 The required syntax for a TCP url is:
 @example