v3.3.0: Accessing from windows is broken

Hi looks like latest build changes broke path separator.

1. Host machine windows
2. code-server machine linux in docker
3. Relevant docker part

RUN go get github.com/derekparker/delve/cmd/dlv
RUN git clone https://github.com/cdr/code-server.git
WORKDIR code-server
RUN git submodule update --init
RUN yarn
RUN yarn vscode
RUN yarn build
RUN yarn build:vscode
RUN yarn release
WORKDIR release
RUN yarn --production
WORKDIR /
ENTRYPOINT node /code-server/release --disable-telemetry  --host 0.0.0.0 --port 3003 

code server is up and running in docker and accessible via 127.0.0.1:3003 on windows host .

Following request fails while ui is loading in browser http://127.0.0.1:3003/vscode-remote-resource?path=\code-server\release\lib\vscode\extensions\theme-defaults\themes\dark_plus.json&tkn=

Checked and confirmed that file is there. changin request to http://127.0.0.1:3003/vscode-remote-resource?path=/code-server/release/lib/vscode/extensions/theme-defaults/themes/dark_plus.json&tkn= returns json data.

[nhooyr]

https://github.com/cdr/code-server/releases/tag/v3.3.1

🎉

[nhooyr]

Will publish a 3.3.1 in the next few hours, just working on #1667