docker: Fix + some tweaks, fixes #155

- Reorder deps & builds
- Download elm binary
- g++ and python3 for node-gyp
- Bump go & alpine versions
- Use npm ci

Dockerfile

@@ -1,22 +1,30 @@
 # Docker build file for Inbucket: https://www.inbucket.org/
 
-# Build
-FROM golang:1.12-alpine3.10 as builder
-RUN apk add --no-cache --virtual .build-deps git make npm
+# Install build-time dependencies
+FROM golang:1.14-alpine3.11 as builder
+RUN apk add --no-cache --virtual .build-deps g++ git make npm python3
 WORKDIR /build
 COPY . .
 ENV CGO_ENABLED 0
 RUN make clean deps
+WORKDIR /build/ui
+RUN rm -rf dist elm-stuff node_modules
+RUN npm ci
+ADD https://github.com/elm/compiler/releases/download/0.19.1/binary-for-linux-64-bit.gz elm.gz
+RUN gunzip elm.gz && chmod 755 elm && mv elm /usr/bin/
+
+# Build server
+WORKDIR /build
 RUN go build -o inbucket \
   -ldflags "-X 'main.version=$(git describe --tags --always)' -X 'main.date=$(date -Iseconds)'" \
   -v ./cmd/inbucket
+
+# Build frontend
 WORKDIR /build/ui
-RUN rm -rf dist elm-stuff node_modules
-RUN npm i
 RUN npm run build
 
 # Run in minimal image
-FROM alpine:3.10
+FROM alpine:3.11
 WORKDIR /opt/inbucket
 RUN mkdir bin defaults ui
 COPY --from=builder /build/inbucket bin