Remove custom test script (and ts-node) when tsd is updated

[pastelmind]

In #20, I added a custom test script (run-tests.ts) to work around a limitation in tsd, our testing tool. Because tsd 0.14.0 does not support the typesVersions property in package.json, it cannot find our typings when invoked from the shell. Since it does not provide any mechanism for specifying a custom type source, we need to temporarily supply a types field in package.json.

To work around this, I wrote a tiny Node.js script (run-tests.ts) that monkey-patches package.json with a types field before running tsd, then restore the original afterwards. I also installed ts-node to avoid an extra compile step when running the script.

The main branch of tsd has recently gained support for custom type sources. Another PR adds an accompanying CLI option for this. If the next release of tsd includes these changes, we may be able to replace this script with an invocation of tsd --typings-file src/index.d.ts.

TODO

• Wait for a new release of tsd
• Update tsd
• Replace custom test script and invoke tsd from the command line instead
• Remove ts-node and/or @types/node