Update Dockerfile

Dockerfile

@@ -4,7 +4,8 @@ ARG FFMPEG_VERSION=latest
 FROM node:alpine as web-builder
 ARG JELLYFIN_WEB_VERSION=master
 RUN apk add curl \
- && cd jellyfin-web \
+ && curl -L https://github.com/jellyfin/jellyfin-web/archive/${JELLYFIN_WEB_VERSION}.tar.gz | tar zxf - \
+ && cd jellyfin-web-* \
  && yarn install \
  && yarn build \
  && mv dist /dist