As of 30 April 2019, NodeJS 6.0 is no longer supported (https://nodejs.org/en/blog/release/v6.17.1/)
This commit updates the engine to the latest lts version which is 10.16.0

It also introduces a `.nvmrc` file to developers who might have to work
on or support services using different versions of node. This is only optional
so shouldn't be an issue.

Addresses some security vulnerablities

Npm audit

Before:
found 17 vulnerabilities (1 low, 5 moderate, 11 high)

After:
found 11 vulnerabilities (1 low, 2 moderate, 8 high)

Updates node version from 6.12 to 10.16 and a couple other dependencies

When exiting `npm start` the following error was raised:

```
TypeError [ERR_INVALID_CALLBACK]: Callback must be a function
    at makeCallback (fs.js:136:11)
    at Object.unlink (fs.js:943:14)
    at process.onInterrupt (/Users/alistairlaing/work/gds-nodejs-boilerplate/start.js:56:6)
    at process.emit (events.js:203:15)
```

unlink is async so it should have a callback.

https://nodejs.org/api/fs.html#fs_fs_unlink_path_callback

Update dependencies and address security notices

Watch for template changes too

Bumps [minimist](https://github.com/substack/minimist) from 1.2.0 to 1.2.2.
- [Release notes](https://github.com/substack/minimist/releases)
- [Commits](https://github.com/substack/minimist/compare/1.2.0...1.2.2)

Signed-off-by: dependabot[bot] <[email protected]>

…-1.2.2

Bump minimist from 1.2.0 to 1.2.2

Bumps [extend](https://github.com/justmoon/node-extend) from 3.0.1 to 3.0.2.
- [Release notes](https://github.com/justmoon/node-extend/releases)
- [Changelog](https://github.com/justmoon/node-extend/blob/master/CHANGELOG.md)
- [Commits](justmoon/node-extend@v3.0.1...v3.0.2)

Signed-off-by: dependabot[bot] <[email protected]>

Bumps [mixin-deep](https://github.com/jonschlinkert/mixin-deep) from 1.3.1 to 1.3.2.
- [Release notes](https://github.com/jonschlinkert/mixin-deep/releases)
- [Commits](jonschlinkert/mixin-deep@1.3.1...1.3.2)

Signed-off-by: dependabot[bot] <[email protected]>

Bumps [fstream](https://github.com/npm/fstream) from 1.0.11 to 1.0.12.
- [Release notes](https://github.com/npm/fstream/releases)
- [Commits](npm/fstream@v1.0.11...v1.0.12)

Signed-off-by: dependabot[bot] <[email protected]>

Bumps [minimist](https://github.com/substack/minimist) from 1.2.2 to 1.2.3.
- [Release notes](https://github.com/substack/minimist/releases)
- [Commits](https://github.com/substack/minimist/compare/1.2.2...1.2.3)

Signed-off-by: dependabot[bot] <[email protected]>

….0.2

Bump extend from 3.0.1 to 3.0.2

…1.0.12

Bump fstream from 1.0.11 to 1.0.12

…-1.2.3

Bump minimist from 1.2.2 to 1.2.3

…ep-1.3.2

Bump mixin-deep from 1.3.1 to 1.3.2