Cast response body to a string for the entire response body.

Signed-off-by: George Steel <[email protected]>

test/MezzioInstallerTest/HomePageResponseTest.php

@@ -174,7 +174,7 @@ public function testHomePageHtmlResponseContainsExpectedInfo(
         self::assertEquals(200, $response->getStatusCode());
 
         // Test response content
-        $html = $response->getBody()->getContents();
+        $html = $response->getBody()->__toString();
 
         self::assertStringContainsString(sprintf('Get started with %s', $containerName), $html);
         self::assertStringContainsString(sprintf('href="%s"', $containerDocs), $html);