message: fix: improve error message
diff: @@ -33,8 +33,12 @@ export class LeanInstaller {
  const filterVersion = /version (\d+)\.\d+\..+/
  const match = filterVersion.exec(stdout)
  if (!match) {
  + if (stdout === 'program not found') {
  + return { version: '', error: `lean4: '${cmd}' program not found.` }
  + } else {
  return { version: '', error: `lean4: '${cmd} ${options}' returned incorrect version string '${stdout}'.` }
  }
  + }
  const major = match[1]
  return { version: major, error: null }
  } catch (err) {
  