Allowed index.ts in tests/fixtures

[ijlee2]

Description

In tsconfig.json, I had excluded tests/fixtures so that TypeScript doesn't compile fixture files (since the fixtures files come from somewhere else and aren't something that I, as the codemod author, own). The index.js files, used to convert the input and output directories to JSONs, are mine, however.

It turned out, it is okay to give these index files the *.ts file extension. With the current TypeScript configuration, the project still compiles correctly before the tests are run.