Fixed: MPL 2 license detection fails when license contains a copyright header

[joshmgross]

A Mozilla Public License can contain a copyright notice before the license header. For example:

Copyright (c) 2014 HashiCorp, Inc.

Mozilla Public License, version 2.0

https://github.com/hashicorp/yamux/blob/v0.1.2/LICENSE#L1-L3

My understanding of the license is that this is valid:

You may add additional accurate notices of copyright ownership.
https://www.mozilla.org/en-US/MPL/2.0/

To resolve that, this allows HeaderMatcher to search the first 3 lines of the license to identify it. This matches the approach used by the MPL 1.1 definition:

LicenseFinder/lib/license_finder/license/definitions.rb

Line 302 in 00b04cb

HeaderMatcher.new(header_regexp_matcher, 2),