Build on install

[elhoyos]

I'm having trouble to npm install on a project using a fork of unleash-client-node because package.json is explicitly stating to never build on install.

#15 seems to be the reason behind it, but filesystem install tests suggests we don't need it anymore.

[coveralls]

Coverage remained the same at 98.226% when pulling 974e325 on elhoyos:build-on-install into b373de6 on Unleash:master.

[ivarconr]

@SimenB any objections?

[SimenB]

I don't think so - I can't remember the issue.

[elhoyos]

Please notice that despite this change works for a working directory installation for both npm install and yarn, it does not work for yarn when used as a github repository.

$ yarn add elhoyos/unleash-client-node#4a85ba6
$ ls -l node_modules/unleash-client/lib # empty
$ rm -rf node_modules
$ yarn
$ ls -l node_modules/unleash-client/lib # empty

This is a yarn issue: yarnpkg/yarn#5235