Bump to go 1.15.12

.drone.yml

@@ -190,7 +190,6 @@ steps:
   environment:
     GCLOUD_AUTH:
       from_secret: gcloud_auth
-    GOLANG: golang:1.16.2-alpine3.12
   commands:
   - dapper ci
   - echo "${DRONE_TAG}-arm" | sed -e 's/+/-/g' >.tags

Dockerfile.dapper

-ARG GOLANG=golang:1.15.8-alpine3.12
+ARG GOLANG=golang:1.15.12-alpine3.12
 FROM ${GOLANG}
 
 ARG http_proxy=$http_proxy

Dockerfile.manifest

-ARG GOLANG=golang:1.15.8-alpine3.12
+ARG GOLANG=golang:1.15.12-alpine3.12
 FROM ${GOLANG}
 
 COPY --from=plugins/manifest:1.2.3 /bin/* /bin/

Dockerfile.test.dapper

-ARG GOLANG=golang:1.15.8-alpine3.12
+ARG GOLANG=golang:1.15.12-alpine3.12
 FROM ${GOLANG}
 
 RUN apk -U --no-cache add bash git gcc musl-dev docker curl jq coreutils python2 openssl

Dockerfile.test.mod.dapper

-ARG GOLANG=golang:1.16.2-alpine3.12
+ARG GOLANG=golang:1.15.12-alpine3.12
 FROM ${GOLANG}
 
 RUN apk -U --no-cache add bash jq