Upgrade to go v1.13.1

Dockerfile.dapper

-FROM golang:1.12.9-alpine3.10
+FROM golang:1.13.1-alpine3.10
 
 RUN apk -U --no-cache add bash git gcc musl-dev docker vim less file curl wget ca-certificates jq linux-headers zlib-dev tar zip squashfs-tools npm coreutils \
     python3 py3-pip python3-dev openssl-dev libffi-dev libseccomp libseccomp-dev make
@@ -29,4 +29,3 @@ WORKDIR ${DAPPER_SOURCE}
 
 ENTRYPOINT ["./scripts/entry.sh"]
 CMD ["ci"]
-

Dockerfile.sonobuoy.dapper

-FROM golang:1.12.9-alpine3.10
+FROM golang:1.13.1-alpine3.10
 
 RUN apk -U --no-cache add bash git gcc musl-dev docker curl jq coreutils
 RUN go get -d github.com/heptio/sonobuoy && \

go.mod

 module github.com/rancher/k3s
 
-go 1.12
+go 1.13
 
 replace (
 	github.com/containerd/btrfs => github.com/containerd/btrfs v0.0.0-20181101203652-af5082808c83