ci: add stage caching to Dockerfile (#408)

Dockerfile

@@ -1,9 +1,10 @@
 FROM node:16 as builder
 
 WORKDIR /build
+COPY web/package.json .
+RUN npm install
 COPY ./web .
 COPY ./VERSION .
-RUN npm install
 RUN DISABLE_ESLINT_PLUGIN='true' REACT_APP_VERSION=$(cat VERSION) npm run build
 
 FROM golang AS builder2
@@ -13,9 +14,10 @@ ENV GO111MODULE=on \
     GOOS=linux
 
 WORKDIR /build
+ADD go.mod go.sum ./
+RUN go mod download
 COPY . .
 COPY --from=builder /build/build ./web/build
-RUN go mod download
 RUN go build -ldflags "-s -w -X 'one-api/common.Version=$(cat VERSION)' -extldflags '-static'" -o one-api
 
 FROM alpine