Upgrade oniguruma to fix security vulnerabilities and allow usage with newer versions of node

[sreuter]

Hey there,

any objections updating the oniguruma to the latest? There's been heaps of security vulnerabilities that have been addressed and also compatibility with newer versions of node.

Cheers!

[sreuter]

See #28

[bhupesh-sf]

When can we expect this to be fixed as we are facing issues in installing the package with latest version of Node JS?