update rustfmt.toml

rustfmt.toml

@@ -2,11 +2,11 @@ unstable_features = true
 
 condense_wildcard_suffixes = true
 format_code_in_doc_comments = true
+group_imports = "StdExternalCrate"
 imports_granularity = "Crate"
 newline_style = "Unix"
 normalize_comments = true
 normalize_doc_attributes = true
-overflow_delimited_expr = false
 reorder_impl_items = true
 spaces_around_ranges = true
 use_field_init_shorthand = true