Update caching library to latest version, updated and fixed phpUnit tests

tests/OfflineTests/COIDParserTest.php

@@ -8,7 +8,7 @@ namespace CloudObjects\SDK;
 
 use ML\IRI\IRI;
 
-class COIDParserTest extends \PHPUnit_Framework_TestCase {
+class COIDParserTest extends \PHPUnit\Framework\TestCase {
 
   public function testRootCOID() {
     $coid = new IRI('coid://example.com');