frictionless 1.2.1

• frictionless now relies on R version 3.6.0 or higher. Originally it stated version 3.5.0 or higher, but this was not tested and likely not true (#238).
• read_package() now returns a warning rather than an error when a datapackage.json contains no resources. This allows use to create the JSON and then add resources with frictionless (#265).
• example_package() now has a version parameter, allowing to load the example Data Package following the Data Package v1 or v2 specification (#249).