message: updated changelog for 3.4
diff: +## 3.4 August 13, 2017
  +
  +- Color values setters at `Template` (`backgroundColor`, `foregroundColor` and `labelColor`) now can accept any valid CSS color string (like 'purple', '#fff', etc) and converts them into `rgb(...)` format that is only acceptable by Apple Wallet pass
  +- `Pass.validate` enforces `rgb()` style values for color fields
  +- `Pass.validate` enforces `webServiceURL` and `authenticationToken` to be either both present or both missing
  +- Exporting `PASS_MIME_TYPE` from `contants`
  +- Added `expirationDate` and `relevantDate` setters and getter to the `Pass` class that accepts both, `Date` or a `string` and converts that to correct W3C date string (or throws if it's impossible)
  +- Added `Pass.addLocation` that accepts point value either as GeoJSON array, `{lat, lng}` or `{ longitude: number, latitude: number, altitude?: number }`
  +
  ## 3.3 August 12, 2017
  - implemented `Pass.transitType()` to set/get transit type for board passes (with values validation and constants)
  