contribution: option to disable path check

[kittems]

Thank you so much for the library!

I ran into an unexpected issue. I did not realize you could pass a path to parse(input, options) and have it load.

I had a .gitignore with only a single line like this:

package-lock.json

And I was surprised to see the parse function returning the contents of my package-lock.json file. This can be inconvenient if not desired (I'd need to append either '#' or '\n' to what I read-in to disable).

I thought it might be nice to add an option to disable path checking. I created a PR that adds the option and a test for it.

// index.js line 32-36
const parse = (input, options = {}) => {
  let filepath = options.path;

  if (isParsed(input)) return input;
  if (!(options.disablePathCheck || false) && isValidPath(input) && fs.existsSync(input)) {
  // ....

// test.js +50-56
  it('should not try to load ignored files as an ignorefile', () => {
    // if our ignore only includes a relative file that happens to be valid (e.g. package.json)
    const content = 'package.json';
    // it should not path check (otherwise would fail)
    const parsed = parse(content, { disablePathCheck: true });
    assert.equal(parsed.patterns, content);
  });

Thank you!