make tests compatible with newer phpunit

tst/I18nTest.php

@@ -189,7 +189,7 @@ class I18nTest extends TestCase
             foreach (array_keys($languages) as $language) {
                 // most languages don't translate the data size units, ignore those
                 if ($messageId !== 'B' && strlen($messageId) !== 3 && strpos($messageId, 'B', 2) !== 2) {
-                    $this->assertStringContains(
+                    $this->assertStringContainsString(
                         $messageId,
                         $languages[$language],
                         "message ID '$messageId' exists in translation file $language.json"

tst/JsonApiTest.php

@@ -287,7 +287,7 @@ class JsonApiTest extends TestCase
         new Controller;
         $content = ob_get_contents();
         ob_end_clean();
-        $this->assertStringContains('id="pasteurl" href="https://example.com/1"', $content, 'outputs shortened URL correctly');
+        $this->assertStringContainsString('id="pasteurl" href="https://example.com/1"', $content, 'outputs shortened URL correctly');
     }
 
     /**
@@ -301,6 +301,6 @@ class JsonApiTest extends TestCase
         new Controller;
         $content = ob_get_contents();
         ob_end_clean();
-        $this->assertStringContains('Error calling YOURLS.', $content, 'outputs error correctly');
+        $this->assertStringContainsString('Error calling YOURLS.', $content, 'outputs error correctly');
     }
 }