fix type parameter of operate in Grouped.reduce
fix type parameter of operate in Grouped.reduce

sunilrebel/scalding,sriramkrishnan/scalding,sriramkrishnan/scalding,rubanm/scalding,avp1984/scalding,tglstory/scalding,chrismoulton/scalding,sriramkrishnan/scalding,jzmq/scalding,aposwolsky/scalding,zirpins/scalding,jzmq/scalding,nkhuyu/scalding,cchepelov/scalding,Chasego/scalding,f7753/scalding,aposwolsky/scalding,bendridi/scalding,danosipov/scalding,AaroC357/scalding,tdyas/scalding,tdyas/scalding,wanyifu/scaldingtest,sid-kap/scalding,benpence/scalding,zirpins/scalding,nvoron23/scalding,MansurAshraf/scalding,stripe/scalding,soundcloud/scalding,f7753/scalding,rubanm/scalding,tresata/scalding,soundcloud/scalding,cauchycui/scalding,cauchycui/scalding,avp1984/scalding,chrismoulton/scalding,rubanm/scalding,sunilrebel/scalding,stripe/scalding,nvoron23/scalding,bendridi/scalding,nkhuyu/scalding,tresata/scalding,bmyerz/scalding,bmyerz/scalding,AaroC357/scalding,vidyar/twitterscalding,MansurAshraf/scalding,piyushnarang/scalding,lucamilanesio/scalding,benpence/scalding,lucamilanesio/scalding,avp1984/scalding,zirpins/scalding,jzmq/scalding,lucamilanesio/scalding,JiJiTang/scalding,sid-kap/scalding,chrismoulton/scalding,piyushnarang/scalding,benpence/scalding,danosipov/scalding,nvoron23/scalding,AaroC357/scalding,cchepelov/scalding,vidyar/twitterscalding,MansurAshraf/scalding,twitter/scalding,epishkin/scalding,tdyas/scalding,bmyerz/scalding,tglstory/scalding,Chasego/scalding,nkhuyu/scalding,aposwolsky/scalding,f7753/scalding,tglstory/scalding,sunilrebel/scalding,bendridi/scalding,tresata/scalding,epishkin/scalding,wanyifu/scaldingtest,cauchycui/scalding,piyushnarang/scalding,sid-kap/scalding,wanyifu/scaldingtest,twitter/scalding,Chasego/scalding,twitter/scalding,soundcloud/scalding,cchepelov/scalding,JiJiTang/scalding,oeddyo/scalding,oeddyo/scalding,danosipov/scalding,JiJiTang/scalding,oeddyo/scalding