node v4 error when using napi_versions/napi_build_versions

Nobody has claimed this yet.

I found that if you add:

```
"package_name": "{module_name}-v{version}-{platform}-{arch}-napi-v{napi_build_version}.tar.gz",
"napi_versions": [
1,
2
]
```

To the `package.json` `binary` property of a node-pre-gyp enabled module it will lead to this error with node v4:

```
./node_modules/.bin/node-pre-gyp rebuild --loglevel=error
/Users/danespringmeyer/projects/node-sqlite3/node_modules/node-pre-gyp/lib/util/napi.js:105
if (!napi_build_versions.includes(napi_version)) napi_build_versions.push(napi_version);
^

TypeError: napi_build_versions.includes is not a function
```

This looks to be because `Array.includes` is not supported with node v4, so we'll either need to use a polyfill or use `Array.indexOf` instead.

@jschlight two questions for you:

- Should we try to support node v4 at all? If not, should this just throw with an easier to understand error?
- If we should support node v4, do you have bandwidth to provide a PR to fix this?

Start with lib/util/napi.js around line 105 and reproduce the package.json binary configuration using the node-pre-gyp rebuild command shown. Determine the project’s Node v4 support policy, then verify that this configuration no longer produces the reported TypeError or gives a clear unsupported-version error.

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