Fix type signature of PolymerBase.splice to accept varargs.
Fix type signature of PolymerBase.splice to accept varargs.

bpowers/PolymerTS,adamcarr/PolymerTS,lgrignon/PolymerTS,adamcarr/PolymerTS,nippur72/PolymerTS,nippur72/PolymerTS,bpowers/PolymerTS,lgrignon/PolymerTS,bpowers/PolymerTS,lgrignon/PolymerTS,adamcarr/PolymerTS