Update source_files and project version in podspec file

[bdesham-vdx]

In commit a842527, the CodableFirebase directory was moved inside a new Sources directory. This PR updates the CocoaPods podspec file to match. (Without this change, CocoaPods will discard all of the source files, thinking that they are unnecessary.)

This PR also updates the project version number to 0.2.2 in the podspec file.