find the closest .gitignore file, parse it, and apply ignore rules.

Given the following .gitignore:

.DS_Store
node_modules
coverage
.nyc_output

const dotgit = require('dotgitignore')()
dotgit.ignore('.DS_Store') // returns 'true'.
dotgit.ignore('README.md') // returns 'false'.

• require('dotgitignore')([opts]): return instance of dotgitignore, optionally configured with opts:
  • opts.cwd: current working directory (defaults to process.cwd()).
• dotgit.ignore(name): returns true if pattern is ignored, false otherwise.