Fixed spelling of "supress" in config option

The spelling of "supress" in the `supress_app_log` configuration option was [not correct](https://www.google.co.uk/search?q=how+to+spell+suppress). As a result, one of our projects ended up suppressing logs when it shouldn't have.

It's our fault for not copy/pasting from the documentation, but it's looks like it may be a very common mistake.

To avoid similar issues in the future, I've fixed the typo, so the supported configuration option is now `suppress_app_log`.

For backward compatibility, `supress_app_log` is still accepted.