swift: fix postinstall build error

[vince-fugnitto]

Description

The following pull-request fixes the theia-swift-docker build caused by the missing postinstall script for the sourcekit-lsp extension: https://github.com/apple/sourcekit-lsp/blob/6511ca732e5957f6ef4f48760e11e7c1643632dc/Editors/vscode/package.json#L23-L28

"scripts": {
    "vscode:prepublish": "npm run compile",
    "compile": "tsc -p ./",
    "watch": "tsc -watch -p ./",
    "createDevPackage": "npm install && ./node_modules/.bin/vsce package -o ./out/sourcekit-lsp-vscode-dev.vsix"
},

How to test

• the CI for the theia-swift-docker image should now successfully pass.

Signed-off-by: vince-fugnitto vincent.fugnitto@ericsson.com

[vince-fugnitto]

@DukeNgn would you mind reviewing?