Support for PHP 8, drop outdated PHP 7.1 and 7.2

See #41.

Thanks to @tbg-jasonfung!

PHP version upgrade

Upgrade php version to ^7.1
Upgrade phpunit version to ^7

0.5.3

Add support fort PHP 7.3

Support SwiftMailer 6

See #37.

Drop PHP 5.4. Support PHP 7.2, CSSToInlineStyles 2.2

Support PHP 7.2 (#30)

* Add PHP 7.2 to the build matrix on Travis CI

* Install various PHPUnit versions

* Exclude PHPUnit 4 from PHP 7.2 build

Drop PHP 5.3, HHVM

• Drop HHVM support 0d24c66 (@hkdobrev)
• Remove unused use statement #19 (@nclsHart)
• Fix tests (@nclsHart)
  • Drop PHP 5.3 support cd839f5
  • Fix indent in fixtures 04569a7
  • Restrict css-to-inline-styles version and update dependencies 5ab4d3c
• Fix tests on libxml < 2.9.5 #22 (@nclsHart)
• Update code style and license #24 (@hkdobrev)

0.4.0: Upgrade CSSToInlineStyles library to 2.0

See #16 for more details.
This is potentially breaking if you pass your own instance of the CSS inliner.

0.3.1: Update tests configuration

• Test on PHP 5.3 again
• Test on PHP 7.1
• Test on lowest and highest possible dependencies as well as on the locked ones
• Set PHPUnit as a dev dependency

See #14 and #15 for more details.

0.3.0

Fix test coverage

0.2.0: Update dependencies and loosen constraints

Merge pull request #6 from barryvdh/patch-2

Update dependencies and improve version constraints