Update test compatibility with phpunit 7

Author: jessarcher

phpunit.xml

@@ -8,7 +8,6 @@
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          verbose="true"
 >
     <testsuites>

tests/TestCase.php

@@ -9,12 +9,12 @@ class TestCase extends PHPUnitTestCase
 {
     public static $functions;
 
-    public function setUp()
+    public function setUp(): void
     {
         self::$functions = Mockery::mock();
     }
 
-    public function tearDown()
+    public function tearDown(): void
     {
         Mockery::close();
     }