Try to reconnect on timeout too

In the case any websocket call takes too long to return and a timeout
was set for the provider to timeout, the provider should try to restart
the connection.

This could happen, for instance, if the client loses connection with the
server, the server closes the connection and later, the connectivity is
up again but since the client did not receive the closing frame *and*
the client does not attempt to send any package to the server, no error
is observed.

`websocket` implementation for Node.js has an option to send keep-alive
frames and detect such scenarios, but the standard browser W3C WebSocket
does not, so it is "vulnerable" to this kind of failure which will
mostly affect web3 subscriptions.

Author: gabmontes

packages/web3-providers-ws/src/index.js

@@ -244,7 +244,13 @@ WebsocketProvider.prototype._addResponseCallback = function(payload, callback) {
         setTimeout(function () {
             if (_this.responseCallbacks[id]) {
                 _this.responseCallbacks[id](errors.ConnectionTimeout(_this._customTimeout));
+
                 delete _this.responseCallbacks[id];
+
+                // try to reconnect
+                if (_this.connection.reconnect) {
+                    _this.connection.reconnect();
+            }
             }
         }, this._customTimeout);
     }