.github/ISSUE_TEMPLATE: fix of a broken link
.github/ISSUE_TEMPLATE: fix of a broken link

to make redirection possible. Changed undercore to dash.

coreos/etcd,ajityagaty/etcd,mkumatag/etcd,mqliang/etcd,dannysauer/etcd,dannysauer/etcd,rnaveiras/etcd,li-ang/etcd,rnaveiras/etcd,mqliang/etcd,ajityagaty/etcd,etcd-io/etcd,mkumatag/etcd,cockroachdb/etcd,gyuho/etcd,mkumatag/etcd,li-ang/etcd,mqliang/etcd,rnaveiras/etcd,etcd-io/etcd,etcd-io/etcd,ajityagaty/etcd,coreos/etcd,cockroachdb/etcd,gyuho/etcd