Tiny fix for the boundary parsing

[sergeypayu]

A better boundary detection that won't fail on such example:
Content-Type: multipart/report;
boundary="----=_Part_2509169_1730566862.1445846478023";
report-type=delivery-status

[djmattyg007]

Hi there. I'm interested in including this change in my fork of this library: https://github.com/djmattyg007/official-library-php-email-parser

Would you be able to explain in a bit more detail what the change is and why it wouldn't work properly in the past? Also, would you be able to add a test email in the tests directory that will only pass with this change?

[sergeypayu]

The change I made addresses the issue with parsing boundary string if there is more data on the line. Like in provided example boundary="----=_Part_2509169_1730566862.1445846478023"; report-type=delivery-status
Before my fix it would have taken the whole string till the end as boundary, while we need only the part between "=" and ";".

[djmattyg007]

I've just pushed a new version of my library that includes this fix. Thanks!