fix: use camel case in generated bin mnemonics

[alex-torok]

#218 added the ability to use the bin name as the default mnemonic for generated package_json.bzl entries. Some generated bin entries have underscores in their name, which is not allowed in action mnemonics.

Without this change, you can get:

Error in run: mnemonic must only contain letters and/or digits, and have non-zero length, was: "webpack_cli"

Use a CamelCase version of the bin name instead.

[alex-torok]

Oops, just realized spaces are a no-go too - Error in run: mnemonic must only contain letters and/or digits, and have non-zero length, was: "webpack cli" I'll see if I can CamelCase the mnemonic.

[gregmagolan]

Sweet. Thanks for the fix. I hit this yesterday as well and Alex started fixing it and then got busy with other things.