Update dependencies

[ddmler]

• Remove support for PHP version 5.6 (it seems we always support the last 3 php versions and so does php-parser)
• Update PHPUnit to version 6.x (needs php 7.0 and up)
• Update php-parser to version 4.x (currently alpha and needs php 7.0 and up)

[kilgaloon]

PHP 5.6 is still widely used, are you sure we want to remove 5.6?

[ddmler]

To be clear this is only the needed php version to run phpsa. You can still check 5.2-5.6 code with it.
And most people won't run phpsa on their production server. More likely in CI, so they could let phpsa run on a higher php version.

Also we probably wait at least until php-parser 4 is stable and not alpha. We need the newest version of this to support the newest php version. At the moment it looks like we still get the new php 7.2 features in the 3.x branch so we don't have to rush this.

[ovr]

Thank @ddmler, cool idea:

Done:

• Remove support for PHP version 5.6 (it seems we always support the last 3 php versions and so does php-parser)
• Update PHPUnit to version 6.x (needs php 7.0 and up)

Didnt:

• Update php-parser to version 4.x (currently alpha and needs php 7.0 and up)

Let's wait for stable release, looks likes this will be in near time 😃

[EvgenyOrekhov]

I tried to fix #348 with #349 but it does not work on PHP <7.1.3.

[EvgenyOrekhov]

I managed to fix #348 without breaking compatibility with PHP 7.0.

[ddmler]

php-parser version 4 is stable released now.
https://github.com/nikic/PHP-Parser/blob/master/UPGRADE-4.0.md
Looks like there a quite a few changes to the node structure so it's gonna be a lot of work to update everything here.

Also after updating tag a new release the last one was more than a year ago.