hack/quickstart: bump the bootkube image to v0.3.7
hack/quickstart: bump the bootkube image to v0.3.7

dghubble/bootkube,ericchiang/bootkube,diegs/bootkube,hongchaodeng/bootkube,diegs/bootkube,kubernetes-incubator/bootkube,diegs/bootkube,ericchiang/bootkube,hongchaodeng/bootkube,ericchiang/bootkube,hongchaodeng/bootkube,kubernetes-incubator/bootkube,dghubble/bootkube,kubernetes-incubator/bootkube,dghubble/bootkube