Fix README.md logo (#1268)

The link to the logo in `README.md` is broken.

Same fix as applied in
hazelcast/hazelcast-nodejs-client#1517

Author: JackPGreen

README.md

@@ -1,6 +1,6 @@
 <p align="center">
     <a href="https://hazelcast.com">
-        <img class="center" width=10% src="https://hazelcast.com/wp-content/themes/hazelcast/img/logo_login.svg" alt="logo">
+        <img class="center" src="https://docs.hazelcast.com/_/img/hazelcast-logo.svg" alt="logo">
     </a>
     <h2 align="center">Hazelcast C++ Client</h2>
 </p>