documentation: clean up a minor syntax issue.

include/SDL3/SDL_filesystem.h

@@ -233,7 +233,7 @@ typedef enum SDL_Folder
  * If NULL is returned, the error may be obtained with SDL_GetError().
  *
  * \param folder The type of folder to find
- * \returns Either a null-terminated C string containing the full path to the
+ * \returns either a null-terminated C string containing the full path to the
  *          folder, or NULL if an error happened.
  *
  * \since This function is available since SDL 3.0.0.