Correct sqlite-to-postgres column mapping

A backend column was added later to the pstat_series table. This commit
reorders the column order to comply with the schema.

database/src/bin/sqlite-to-postgres.rs

@@ -290,8 +290,8 @@ struct PstatSeriesRow<'a> {
     krate: &'a str,
     profile: &'a str,
     scenario: &'a str,
-    backend: &'a str,
     metric: &'a str,
+    backend: &'a str,
 }
 
 impl Table for PstatSeries {
@@ -314,8 +314,8 @@ impl Table for PstatSeries {
                 krate: row.get_ref(1).unwrap().as_str().unwrap(),
                 profile: row.get_ref(2).unwrap().as_str().unwrap(),
                 scenario: row.get_ref(3).unwrap().as_str().unwrap(),
-                backend: row.get_ref(4).unwrap().as_str().unwrap(),
                 metric: row.get_ref(5).unwrap().as_str().unwrap(),
+                backend: row.get_ref(4).unwrap().as_str().unwrap(),
             })
             .unwrap();
     }