Fix comment formatting.

The module comment should use "//!" instead of "///". Otherwise, it is
considered to apply to the *next* thing, in this case the "use" statement
that follows, not the file as whole. "cargo fmt" revealed this by insisting
to move the "use crate::pg_constants" line to before the comment.

postgres_ffi/src/relfile_utils.rs

@@ -1,8 +1,8 @@
-///
-/// Common utilities for dealing with PostgreSQL relation files.
-///
-use regex::Regex;
+//!
+//! Common utilities for dealing with PostgreSQL relation files.
+//!
 use crate::pg_constants;
+use regex::Regex;
 
 #[derive(Debug, Clone, thiserror::Error, PartialEq)]
 pub enum FilePathError {