Update Docker image to Alpine 3.13

Dockerfile

@@ -1,9 +1,4 @@
-FROM golang:1-alpine3.12 AS builder
-
-RUN echo $'\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/main\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/testing\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/community' >> /etc/apk/repositories
+FROM golang:1-alpine3.13 AS builder
 
 RUN apk add --no-cache git ca-certificates build-base su-exec olm-dev
 
@@ -11,17 +6,12 @@ COPY . /build
 WORKDIR /build
 RUN go build -o /usr/bin/mautrix-whatsapp
 
-FROM alpine:3.12
-
-RUN echo $'\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/main\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/testing\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/community' >> /etc/apk/repositories
+FROM alpine:3.13
 
 ENV UID=1337 \
     GID=1337
 
-RUN apk add --no-cache ffmpeg su-exec ca-certificates olm bash jq yq@edge curl
+RUN apk add --no-cache ffmpeg su-exec ca-certificates olm bash jq yq curl
 
 COPY --from=builder /usr/bin/mautrix-whatsapp /usr/bin/mautrix-whatsapp
 COPY --from=builder /build/example-config.yaml /opt/mautrix-whatsapp/example-config.yaml

Dockerfile.ci

@@ -1,14 +1,9 @@
-FROM alpine:3.12
-
-RUN echo $'\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/main\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/testing\n\
-@edge http://dl-cdn.alpinelinux.org/alpine/edge/community' >> /etc/apk/repositories
+FROM alpine:3.13
 
 ENV UID=1337 \
     GID=1337
 
-RUN apk add --no-cache ffmpeg su-exec ca-certificates bash jq curl yq@edge
+RUN apk add --no-cache ffmpeg su-exec ca-certificates bash jq curl yq
 
 ARG EXECUTABLE=./mautrix-whatsapp
 COPY $EXECUTABLE /usr/bin/mautrix-whatsapp