Updates dependencies

[perploug]

Updates package dependencies to their latest versions to patch security issues.

• Updated dependencies and devdependencies in package.json
• Updated the test coverage to nyc from instanbul
• Tests are passing

[tallbrick]

@perploug it looks like you'll need to update the Travis CI config files to be compatible with your changes (note the above build errors). const and let weren't supported until at least Node v6.0.0.

You should consider updating this property in the .travis.yml:

node_js:
- '8.0.0'
- '7.0.0'
- '6.0.0'
- iojs

Of course you could also use more recent node versions as well...
https://node.green/

[tallbrick]

@marcellodesales

This PR resolves some nasty vulerabilities (which puts the ongoing use of this lib in question). Any chance you could review this one?

[marcellodesales]

@tallbrick I will get to it during hacktoberfest!

[marcellodesales]

@tallbrick @perploug any interest in updating the travis build with the recent versions of node? I can merge this PR soon after the build passes...

[marcellodesales]

Done on #16