Bump container to 1.21

Dockerfile

@@ -1,11 +1,11 @@
-FROM golang:1.18-alpine3.16 AS builder
+FROM golang:1.21-alpine AS builder
 RUN apk --no-cache add git
 COPY . /build/
 WORKDIR /build
 ENV CGO_ENABLED 0
 RUN go build -o ans -ldflags "-s -X 'main.VERSION=$(git describe --tags)' -X 'main.BUILDDATE=$(date +'%Y-%m-%dT%H:%M:%S')'"
 
-FROM alpine:3.16
+FROM alpine:3
 RUN apk --no-cache add ca-certificates bash bash-completion
 COPY --from=builder /build/ans /bin/ans
 RUN echo "source /usr/share/bash-completion/bash_completion" >> ~/.bashrc