Update npmignore and files package

[friederbluemle]

A quick update to .npmignore and the files section in package.json that reduces the distribution artifact size by more than 70% (mainly by no longer including Gradle wrapper, which is not used by app consumers).

Before:

npm notice name:          react-native-keychain
npm notice version:       4.0.0
npm notice filename:      react-native-keychain-4.0.0.tgz
npm notice package size:  79.7 kB
npm notice unpacked size: 172.2 kB
npm notice total files:   31

After:

npm notice name:          react-native-keychain
npm notice version:       4.0.0
npm notice filename:      react-native-keychain-4.0.0.tgz
npm notice package size:  22.9 kB
npm notice unpacked size: 103.8 kB
npm notice total files:   22

CC @SaeedZhiany

[friederbluemle]

Rebased.

[friederbluemle]

@vonovak - For the merge, by any change could you use a regular merge? My commit is GPG signed, and I would prefer it not to be rewritten on the GitHub server (or having to force delete my local branch). I just rebased my branch onto the latest master.

[oblador]

This doesn't include some pretty important files like the index.js. Did you test to use the package with these settings?

[friederbluemle]

@oblador - index.js is defined as main in package.json. Along with a few other essential files, it is always included in the packed file. More info about this mechanism here: https://docs.npmjs.com/misc/developers#keeping-files-out-of-your-package
Yes, I tested this and you can easily do it too: Just run npm pack and observe the output :)

[oblador]

OK, fair enough, i'll give it a try myself too then. Any reason we can't get rid of the .npmignore fully btw?

[friederbluemle]

@oblador - Great question. Because of the typical setup of a RN library that contains nested app project the dependency resolution with Yarn may be tricky. There is some inconsistency in the way RN library example projects include the library they're showcasing (some use a NPM reference, some a relative path, some other babel/metro hacks). It is true that with the current setup the npmignore file could be removed. I have some local changes with other updates that might require the file to be re-added though. In order to avoid that I kept it for now. We can always fully remove it later. Please let me know if this is okay.
Rebased again.

[vonovak]

Thanks for the explanation, I think this sounds good :)