closes #376

let's embrace the future @kylebarron and depends on features that were added in python 3.9 😄

summary

• in use importlib.resources to find the cmap_data directory #370 we switched to importlib.resources.path() to find the path for rio_tiler/cmap_data.
• ☝️ worked in python 3.7 and 3.8 ... but failed in 3.9. The docs did mention that the second argument of path() had to be a file ... but it worked with a directory... it's not the case anymore with 3.9
• A new methods (.files()) was added to 3.9, and it gives the result we were hopping for.

importlib.resources.files(package)
Returns an importlib.resources.abc.Traversable object representing the resource container for the package (think directory) and its resources (think files). A Traversable may contain other containers (think subdirectories).
package is either a name or a module object which conforms to the Package requirements.
New in version 3.9.