v0.8.2 bug fix

v0.8.1: shellcheck fix

dapp v0.8

dapp testnet: use geth --dev from 1.7.3

This makes `dapp test-geth-experimental` faster because of insta-mining.

Note that in order to run realistic dapp test suites, we need a patched
geth as provided by the DappHub Nix channel, in order to increase the
default block gas limit (which is hard-coded).