Update overrides.md

Author: kyle-leonhard

doc/user-guide/src/overrides.md

@@ -122,8 +122,8 @@ string in the following form:
 ```
 (<channel>[-<date>])|<custom toolchain name>
 
-<channel>       = stable|beta|nightly|<versioned>
-<versioned>     = <major.minor>[-<beta tag>]|<major.minor.patch>[-<beta tag>]
+<channel>       = stable|beta|nightly|<versioned>[-<beta tag>]
+<versioned>     = <major.minor>|<major.minor.patch>
 <beta tag>      = beta[.<number>]
 <date>          = YYYY-MM-DD
 ```