exchange_rate: minor clean-up
exchange_rate: minor clean-up

based on mhsmith/electrum@7ed3f032dd90210638a6efa4b513350d2824037a

spesmilo/electrum,neocogent/electrum,fujicoin/electrum-fjc,fujicoin/electrum-fjc,pooler/electrum-ltc,neocogent/electrum,wakiyamap/electrum-mona,neocogent/electrum,vialectrum/vialectrum,vialectrum/vialectrum,wakiyamap/electrum-mona,spesmilo/electrum,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,fujicoin/electrum-fjc,spesmilo/electrum,pooler/electrum-ltc,vialectrum/vialectrum,pooler/electrum-ltc,pooler/electrum-ltc