Add missing word

Author: matthiasbeyer

doc/src/overrides.md

@@ -96,7 +96,7 @@ specified. `channel` and `path` are mutually exclusive.
 
 For backwards compatibility, `rust-toolchain` files also support a legacy
 format that only contains a toolchain name without any TOML encoding, e.g.
-just `nightly-2021-01-21`. The file has to be encoded in US-ASCII this case
+just `nightly-2021-01-21`. The file has to be encoded in US-ASCII in this case
 (if you are on Windows, check the encoding and that it does not start with a
 BOM). The legacy format is not available in `rust-toolchain.toml` files.