Updates license from GPL to LGPL

[balazsnasz]

LGPL license allows this package to be used in a different (proprietary) licensed projects without having to make its source code available, while keeping the mysql-import library open source.

With GPL-3.0 license, if someone uses the mysql-import package in their project, it MUST be also GPL license and must share the source code. Explanation here: https://www.gnu.org/licenses/gpl-faq.html#IfLibraryIsGPL

That's why I'm proposing a change to the LGPL license.