Update `.gitattributes` `export-ignore` rules
Update `.gitattributes` `export-ignore` rules

 - Adds `.github` directory to `.gitattributes` file with an `export-ignore` rule.
 - This also aligns all `export-ignore` rules for more readability.
 - Removes `.travis.yml` file that is no longer used.

nikic/PHP-Parser,nikic/PHP-Parser