Fix implode() PHP 7.4 (ThingEngineer#870)

implode(): Passing glue string after array is deprecated.

Author: harryqt

MysqliDb.php

@@ -1835,7 +1835,7 @@ protected function _buildInsertQuery($tableData)
         $dataColumns = array_keys($tableData);
         if ($isInsert) {
             if (isset ($dataColumns[0]))
-                $this->_query .= ' (`' . implode($dataColumns, '`, `') . '`) ';
+                $this->_query .= ' (`' . implode('`, `', $dataColumns) . '`) ';
             $this->_query .= ' VALUES (';
         } else {
             $this->_query .= " SET ";