Added a TypeScript definition, updated vulnerable devDependencies

[EvanDarwin]

Added a TypeScript definition file. I also updated some devDependencies that had vulnerabilities.

[EvanDarwin]

It looks like this is failing on node <0.12 because of mocha. This shouldn't affect actual production environments however. Can we remove those test versions, and add node 10, 11, and 12?

[AgainPsychoX]

@jonschlinkert PTAL, I really would like use something like this in my project.

[itschip]

This should be approved bro