fix: docker base image needs be at latest node:14-alpine

[hangxingliu]

Hi, I tested use this tools in Docker yesterday and I got the error output:

/opt/vsce/out/package.js:136
    return (translations ?? [])
                          ^

SyntaxError: Unexpected token '?'
    at wrapSafe (internal/modules/cjs/loader.js:915:16)
    at Module._compile (internal/modules/cjs/loader.js:963:27)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)
    at Module.load (internal/modules/cjs/loader.js:863:32)
    at Function.Module._load (internal/modules/cjs/loader.js:708:14)
    at Module.require (internal/modules/cjs/loader.js:887:19)
    at require (internal/modules/cjs/helpers.js:74:18)
    at Object.<anonymous> (/opt/vsce/out/main.js:27:19)
    at Module._compile (internal/modules/cjs/loader.js:999:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1027:10)

After I read the document and source codes. I found the Node.js version in the Dockerfile is not suitable for the requirement in the README file.
So I updated it from 12 to 14.

Thanks.

[sanemat]

@joaomoreno Do you have any concerns?

[github-actions]

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