fix: move sql to error stack (#8)

Author: fengmk2

lib/operator.js

@@ -49,7 +49,7 @@ proto.query = function* (sql, values) {
   try {
     return yield this._query(sql);
   } catch (err) {
-    err.message += ' (sql: ' + sql + ')';
+    err.stack = err.stack + '\n    sql: ' + sql;
     debug('query error: %s', err);
     throw err;
   }

test/client.test.js

@@ -212,6 +212,7 @@ describe('test/client.test.js', function () {
         // error, rollback
         yield conn.rollback(); // rollback call won't throw err
         assert.equal(err.code, 'ER_PARSE_ERROR');
+        assert(/sql: insert into/.test(err.stack), err.stack);
       } finally {
         // should release connection whatever
         conn.release();