[BTCChina] Remove null from signature message.
Merge pull request #654 from sutra/develop

[BTCChina] Remove null from signature message.
[Poloniex] Switched Ticker volume to baseSymbol
[MintPal] Switched Ticker volume to baseSymbol
Merge pull request #655 from zholmes1/develop

Fixed Ticker volume currency on Poloniex and MintPal