proxy authentification fix (#274)

using a proxy with username and password authentification needing the username:password being base64 encoded

Syntax:
Proxy-Authorization: <type> <credentials>
example: 
Proxy-Authorization: Basic YWxhZGRpbjpvcGVuc2VzYW1l



this fix

Author: devgianlu

lib/src/main/java/xyz/gianlu/librespot/core/Session.java

@@ -1229,10 +1229,8 @@ static ConnectionHolder create(@NotNull String addr, @NotNull Configuration conf
                     DataInputStream in = new DataInputStream(sock.getInputStream());
 
                     out.write(String.format("CONNECT %s:%d HTTP/1.0\n", apAddr, apPort).getBytes());
-                    if (conf.proxyAuth) {
-                        out.write("Proxy-Authorization: Basic ".getBytes());
-                        out.write(Base64.getEncoder().encodeToString(String.format("%s:%s\n", conf.proxyUsername, conf.proxyPassword).getBytes()).getBytes());
-                    }
+                    if (conf.proxyAuth)
+                        out.write(String.format("Proxy-Authorization: %s\n", Credentials.basic(conf.proxyUsername, conf.proxyPassword)).getBytes());
 
                     out.write('\n');
                     out.flush();