Never exclude package.json, even when specified in excludeGlobs.

[droustchev]

If someone specifies *.json or even package.json via the excludeGlobs, the npm install step in the tmp folder will fail due to ENOPACKAGEJSON. This PR modifies the rsync command to always include the package.json, similar to how certain files are always excluded.

[DeviaVir]

This behaviour should also keep --prebuiltDirectory in mind (https://github.com/motdotla/node-lambda#prebuilt-packages)

i.e. only exclude package.json from excludes when --prebuiltDirectory is not set

[droustchev]

I'll try update the PR! Didn't use --prebuiltDirectory, hence I didn't notice my change breaking existing behaviour.

[droustchev]

I added a commit which addresses the concern around --prebuiltDirectory, i.e. if said flag is set, rsync will be called without the --include package.json.
Presumably, a prebuilt directory shouldn't have a package.json though, or? Let me know if more changes are required.

[DeviaVir]

Perfect! Thanks for your contribution, I'll include it in the next release.