Tags with the letter n in them are not purged

[mdickopp]

Tags that have the letter n in them (e.g. input, main) are not purged.

Code to reproduce:

const Purgecss = require('purgecss');

const purgecss = new Purgecss({
  content: [{
    raw: '<h1></h1>',
  }],
  css: [{
    raw: 'h1 { margin: 0; } h2 { margin: 0; } input { margin: 0; }'
  }]
});

console.log(purgecss.purge()[0].css);

Expected output:

h1 { margin: 0; }

Actual output:

h1 { margin: 0; } input { margin: 0; }

I think that the regular expression in line 328 in src/index.js might be the culprit, since it matches tags that have an n in them.