Auto merge of rust-lang#15295 - bernardosulzbach:fix-ssr-help-message, r=lnicola

Fix rust-analzyer ssr help message

It's missing a `>`, so

```
> rust-analyzer ssr '''$a.foo($b) ==> bar($a, $b)'''
can't parse `rule`, Parse error: Cannot find delimiter `==>>`
```

happens.

Author: bors

crates/rust-analyzer/src/cli/flags.rs

@@ -113,7 +113,7 @@ xflags::xflags! {
         }
 
         cmd ssr {
-            /// A structured search replace rule (`$a.foo($b) ==> bar($a, $b)`)
+            /// A structured search replace rule (`$a.foo($b) ==>> bar($a, $b)`)
             repeated rule: SsrRule
         }