fix outdated docu
fix outdated docu

was still referring to Signal.Input instead of Signal.Channel
laszlopandy/core,avh4/elm-lang-core,Pisys/core,bradurani/core,slava-sh/core,suryagaddipati/core,alexiamcdonald/elm-core,simonh1000/core,martinos/core,Dandandan/core,rgrempel/core,ThomasWeiser/core,vilterp/core,krisajenkins/core,deadfoxygrandpa/core,ThomasWeiser/core,deadfoxygrandpa/core,isaacsanders/core,avh4/elm-lang-core,suryagaddipati/core,bradurani/core,Pisys/core,laszlopandy/core,eeue56/core,colinmccabe/core,colinmccabe/core,vilterp/core,Dandandan/core,rick68/core,manleyjster/core,martinos/core,rick68/core,isaacsanders/core,simonh1000/core,alexiamcdonald/elm-core,krisajenkins/core,rgrempel/core,manleyjster/core,eeue56/core