QueryBuilder multiply and divide support

[faissaloux]

Hello 👋🏻

In this PR I have added multiply and divide to QueryBuilder .

Usage

DB::table('users')->where('name', 'John Doe')->multiply('salary');    // "salary" * 1
DB::table('users')->where('name', 'John Doe')->multiply('salary', 2); // "salary" * 2
DB::table('users')->where('name', 'John Doe')->divide('salary');      // "salary" / 1
DB::table('users')->where('name', 'John Doe')->divide('salary', 2);   // "salary" / 2

Checklist

• Add tests and ensure they pass