Added security section: The importance of having developers embrace security is growing, and I believe every (awesome) list of this nature should have a security section enumerating security tools.
Added snyk: I kicked off the section with snyk, which holds your hand through finding vulnerable npm dependencies and fixing them through guided upgrades or patches, as well as adding that to your build so you don't accidentally add vulnerable dependencies later on.
It's worth noting that while Snyk is a company, the client & vulnerability DB is open source (https://github.com/Snyk/vulndb), and the testing & patching functionality is forever free.
Full disclosure: I'm a part of the Snyk team, on a mission to help make open source more secure! ;)
Closes#491
