reset base64-js dependency version to ~0.0.4 because feross's upstream PR was accepted.

Hey feross, is it cool with you if we reset this?  I'm trying to install native-buffer-browserify and getting some errors related to this version number.  Possible that the root cause is unrelated (read: I've never used npm before and have basically no idea what I'm doing), but this seems like positive cleanup to do in any case.

Thanks!