message: ADD install step after adding script & dependency to package.json
diff: +import { spawn } from 'cross-spawn';
  import fetch from 'node-fetch';
  import { pathExists } from 'fs-extra';
  import path from 'path';
  @@ -540,6 +541,19 @@ export async function runTest({
  If you would still prefer not to check it into source control, you can remove it from 'package.json' and set it via an environment variable instead.
  `
  );
  +
  + // now actually install cross-env
  + const npmPath = process.env.npm_execpath;
  + const npmPathIsJs = typeof npmPath === 'string' && /\.m?js/.test(path.extname(npmPath));
  + const execPath = npmPathIsJs ? process.execPath : npmPath || 'npm';
  +
  + // Run either:
  + // npm/yarn install (depending on npm_execpath)
  + // node path/to/npm.js install (if npm run via node)
  + spawn(execPath, [...(npmPathIsJs ? [npmPath] : []), 'install'], {
  + cwd: process.cwd(),
  + ...{ stdio: 'inherit' },
  + });
  } else {
  log.info(
  dedent`
  