[Composer] Bump guzzlehttp/guzzle to version 7 to suppress deprecation notices

- Bump divineomega/password_exposed to version 3 to remove dependency on Guzzle version 6
- Add new ICanHandleHttpResponses->getBodyString method to solve inheritance mismatch with GuzzleHttp\Psr7\ResponseInterface->getBody return type

src/Module/OStatus/PubSubHubBub.php

@@ -154,7 +154,7 @@ class PubSubHubBub extends \Friendica\BaseModule
 		$separator    = parse_url($hub_callback, PHP_URL_QUERY) === null ? '?' : '&';
 
 		$fetchResult = $this->httpClient->fetchFull($hub_callback . $separator . $params);
-		$body        = $fetchResult->getBody();
+		$body        = $fetchResult->getBodyString();
 		$returnCode  = $fetchResult->getReturnCode();
 
 		// give up if the HTTP return code wasn't a success (2xx)

src/Module/OStatus/Subscribe.php

@@ -96,7 +96,7 @@ class Subscribe extends \Friendica\BaseModule
 					return $o . $this->t('Couldn\'t fetch friends for contact.');
 				}
 
-				$friends = $curlResult->getBody();
+				$friends = $curlResult->getBodyString();
 				if (empty($friends)) {
 					$this->pConfig->delete($uid, 'ostatus', 'legacy_contact');
 					return $o . $this->t('Couldn\'t fetch following contacts.');