encodes incorrectly when query string has a `+` symbol

[pasangsherpa]

This is probably because we're passing in an un-encoded string as an input to querystring.parse() function in line 13

Looks like querystring.parse() function takes an encoded string, and in line 55 of the library, + symbol is replaced with %20. This makes sense because when encoding a space, it is sometimes encoded as + or %20.

However, in our case + is the raw value and we wan't it to be treated as a + and not a space

Expected behavior No matter how you pass the query parameters (object or string), it should always produce the same result

Actual behavior Query parameters which includes + symbol if passed in as string, gets encoded as %20 instead of %2B

test('should encode a url if encodeComponents is truthy when passed query as either object or string', function (t) {
  t.plan(2)

  var token = '0_h5E0i+IAmI8aZXOPEbgAWMiTA='
    , expected = 'http://example.com/?token=' + encodeURIComponent(token)

  // query object includes `+` symbol
  var result1 = appendQuery('http://example.com/', { token: token } , { encodeComponents: true })
  t.equal(result1, expected, 'should be equal')

  // query string includes `+` symbol
  var result2 = appendQuery('http://example.com/', 'token=' + token, { encodeComponents: true })
  t.equal(result2, expected, 'should be equal') 
})

[lakenen]

Thanks for submitting this issue. I don't have time to come up with a fix right now, but if you send a PR I'd be happy to take a look and merge.