Fix/phpunit 8

[shijij]

Reason

Function ReflectionType::__toString() is deprecated Error while running unit test with php7.4, blocking further contributions.

Work performed

• Update composer.json and composer.lock
• PhpUnit 8 changes
  • add return type for setUp()
  • suppress no assertion performed error for data providers.
  • replace getMockBuilder with createMock (for disableOriginalConstructor())
• CI: move PHP 7.0 and 7.1 to allow_failures. since PHP>= 7.2.5 is required from the Guzzle update Update to Guzzle 7 #143

[ssicard]

Completed in #275