Fix package.json

Nice to see that you had the time to tackle this! I've just fixed a few things in the package.json file that caught my eye:

 - Package names may only contain letters, numbers, dashes and unterscores (dub should enforce that, but maybe a check is missing somewhere)
 - The "version" field is obsolete and not used anymore (versions are inferred from the git branch/tag names)
 - "dflags" expects an array