Fix `Goto()` application documentation

[7-zete-7]

On documentation syntax is Goto([context,[extensions,]]priority), but in real syntax is Goto([[context,]extension,]priority) (see https://github.com/asterisk/asterisk/blob/master/main/pbx.c#L8841C51-L8841C83).

[gtjoseph]

Yeah, I think Gosub is also broken. I'm looking at the build scripts to see where the issue might be. .