Implement insert on borrow to prevent move

Otherwise the record can't be used anymore after calling its insert
method.

src/main.rs

@@ -64,7 +64,7 @@ impl Record {
         }
     }
 
-    fn insert(self, conn: &rusqlite::Connection) -> Result<usize, TTError> {
+    fn insert(&self, conn: &rusqlite::Connection) -> Result<usize, TTError> {
         conn.execute(
             "INSERT INTO Timestamps VALUES (?1, ?2)",
             &[&self.timestamp.naive_local(), &self.state],