Location of version property is inconsistent between core APIs

[not-an-aardvark]

In ESLint 4.6.1, we have a version property on CLIEngine and Linter indicating the version of ESLint being used. However, the version property appears in different places; it's placed on CLIEngine directly, but it's placed on instances of Linter.

const eslint = require("eslint");

eslint.CLIEngine.version // 4.6.1
eslint.Linter.version // undefined

new eslint.CLIEngine().version // undefined
new eslint.Linter().version // 4.6.1

This happened because the version property was added when Linter was a singleton rather than a constructor, so users were previously expected to access eslint.linter.version.

This could be mildly annoying; for example, an integration that only has access to Linter (like https://eslint.org/demo) would need to create a throwaway instance of Linter to get the version.

I propose that we add version as a static property of Linter. We could also copy it to Linter.prototype to prevent integrations from breaking if they were checking for the version property on instances.

[nzakas]

Looks like everyone thought this was a good idea and it just fell through the cracks. I'll tackle this.