Improve stuffs about PHPUnit setting and assertion

[peter279k]

Changed log

• Migrating the PHPUnit configuration to resolve following warning message:

Warning:       Your XML configuration validates against a deprecated schema.
Suggestion:    Migrate your XML configuration using "--migrate-configuration"!

• Adding the Luur\Amplitude\Tests; namespace for these testing classes.
• Using the assertIsInt to assert expected type is integer.
• Using the assertIsFloat to assert expected type is float.
• Using the assertIsString to assert expected type is string.
• Using the assertIsArray to assert expected type is array.