Strip trailing whitespace in files (#4575)

* Strip trailing whitespace in rs files

* Strip trailing whitespace in toml files

* Strip trailing whitespace in md files

* Strip trailing whitespace in nu files

docs/commands/flatten.md

@@ -18,7 +18,7 @@ Flatten the table.
 
 flatten a table
 ```shell
-> [[N, u, s, h, e, l, l]] | flatten 
+> [[N, u, s, h, e, l, l]] | flatten
 ```
 
 flatten a table, get the first item