Switching library for Slack client

As "maknz/slack" is not maintained anymore, forked library "alek13/slack" is now used.

option "webhook" will throw exception when missing

Bug: Silent Dead if webhook url missing (#13)

* Correct Indentation

* Add Exception if webhook is missing

Co-authored-by: Danny Linden <d.linden@ryte.com>

added new option: "extendedMaxErrors"

You can now limit the number of shown errors in mode extended: true by adding option extendedMaxErrors in config of extension.

1.5.1

• fix: removed Codeception v3.x from dependencies so that users of Codeception v2.x can also use it

1.5.0 - option "webhook" now optional

++ changed behavior: option "webhook" is now optional.
Before it was required and threw an exception when left empty. Now it will just not publish any test result without complaining.
++ minor code refactoring without impact

1.4.3

fix for PHPUnit TestResult class

fix for "channelOnFail"

1.4.2

fix for 'channelOnFail'

fix for when "channelOnFail" is empty

1.4.1

-- fix: "channelOnFail" (dont use it when it's empty)

1.4.0

feature: new optional config key "channelOnFail". When you specify a value for this config key, in case of failure all messages will be sent to this list of channels (f.e. channelOnFail: '#alerts,@user.abc')

1.3.0

• feature: new strategy "successonly". In this strategy slack messages will only be sent when the test run was a success.