cloud: add Dave Day to contributors
cloud: add Dave Day to contributors

Change-Id: I5f9b18bbe66bda176ecbcbddd1c36d64ddca10f6

ptomasroos/gcloud-golang,Maksadbek/gcloud-golang,googleapis/google-cloud-go,blowmage/gcloud-golang,michael-grosshans/google-cloud-go,roth1002/gcloud-golang,Maksadbek/gcloud-golang,roth1002/gcloud-golang,michael-grosshans/google-cloud-go,googleapis/google-cloud-go,hsinhoyeh/gcloud-golang,hsinhoyeh/gcloud-golang,ptomasroos/gcloud-golang,googleapis/google-cloud-go,blowmage/gcloud-golang,googleapis/google-cloud-go