Symbol unvailable: suggest for replacement

We are using hooked provider and lightwallet libs for our mobile wallet LETH (https://github.com/inzhoop-co/LETH) and we find some issues using Symbol on android devices.

```
In hooked-web3-provider.js
row 49: ... requests[Symbol.iterator]() ...
```

Symbol is unvailable for more devices so we suggest a fix with a replacement using forEach, like this :

```
requests.forEach(function(request) {
if (request.method == "eth_sendTransaction") {
throw new Error("HookedWeb3Provider does not support synchronous transactions. Please provide a callback.");
}
```

Look at our version on github for complete file:
https://github.com/inzhoop-co/LETH/blob/master/www/lib/thirdparty/hooked-web3-provider.js

Great work!