don't throw when buildifier is not found

[Toxicable]

We'd like to just use this extension for code highlighting. So we don't need to have buildifier or bazel installed globally on our systems. Possibly adding config to disable this behaviour would suffice

[eltix]

Yes this would very much appreciated. This extension is currently unusable without buildifier installed. VScode hangs forever upon file saving.

[zopsicle]

A workaround for syntax highlighting is to uninstall the extension and exploit the similarity between Skylark and Python, and put the following in your VS Code configuration file:

"files.associations": {
    "BUILD": "python",
    "WORKSPACE": "python",
    "*.bzl": "python",
}