Add return type to ResetInterface implementations (#1371)

Author: nicolas-grekas

src/Credentials/CacheProvider.php

@@ -38,7 +38,7 @@ public function getCredentials(Configuration $configuration): ?Credentials
         return $this->cache[$key];
     }
 
-    public function reset()
+    public function reset(): void
     {
         $this->cache = [];
     }

src/Credentials/ChainProvider.php

@@ -60,7 +60,7 @@ public function getCredentials(Configuration $configuration): ?Credentials
         return null;
     }
 
-    public function reset()
+    public function reset(): void
     {
         $this->lastSuccessfulProvider = [];
     }