Bugfix: Fixing issues with falsy values in format

[knicefire]

Fixing issues

• In case a value is undefined the { symbol is rendered instead of leaving it as is
• In case a value is falsy (0, '', null, false) the { is rendered instead of the value itself

Testing framework

• Added mocha testing framework
• Added tests for formatter

Git hook

• Enforcing of npm test on pre-push via magic of husky

[AndiDittrich]

Hi @knicefire

thanks for your contribution.

the changes to the formatter are ok but i didn't confirm with the testcases/libs

---

therefore please apply the following changes:

• remove chai and husky
• move the required test configurations test/_defaults.js into the test file
• use name.test.js for all testcases
• use standard assert library

example: https://github.com/AndiDittrich/Node.fs-magic/blob/master/test/mkdirp.test.js

[knicefire]

@AndiDittrich
Thanks for the quick reaction and the feedback.

You are right I shouldn't have assumed that adding husky and chai is something the project really needed.

I've done all the required updates listed above.