gnosis / dex-services / 5153

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travis-pro

Automatically determine chain id through web3 (#1416)

instead of having to specify it on the command line.

For the contract using the chain id instead of network id is what was
intended anyway and for the gas station it doesn't matter whether we
match on network id or chain id because they are the same for mainnet
and rinkeby.

Based on Felix' suggestion.

### Test Plan
Added a debug print to the gas station to see which chain id is used and tried it with mainnet and rinkeby node url.

13023 of 53721 branches covered (24.24%)

Branch coverage included in aggregate %.

3446 of 5433 relevant lines covered (63.43%)

43560.03 hits per line