Rename config to config.toml

[sabify]

.toml extension is needed based on the documentation.

[Noah-Kennedy]

Not really.

Note: Cargo also reads config files without the .toml extension, such as .cargo/config. Support for the .toml extension was added in version 1.39 and is the preferred form. If both files exist, Cargo will use the file without the extension.

[Noah-Kennedy]

Even though it isn't strictly necessary, since config.toml is the preferred name now I see no reason not to do this.