Fix spelling

A simple spelling fix, that annoyed me each time I stumble over it.

This is a test if you agree to such changes. Dunno if spelling fixes fall under the "we fix when we touch the file for other reasons" - category.

I'd like to see this backported to at least 2-3-stable. (Want to bring our diff to zero)
@JDutil Good catch. fixed. I'm not a native speaker and my brain passes by some ugly English without interrupt ;)