Add USDC to allowed symbols for ccxt

[skirsch]

// see a sample bug report here: #1

Describe the bug

// A succinct description of the buggy behavior.
// This section includes what the bot is doing and why you think it is incorrect.

The bot aborts if use USDC.

Expected behavior

// A succinct description of what you expected to happen.

I think the correct behavior in this situation is for the bot to not crash

Frequency

The frequency is: always

Steps To Reproduce

Possible Solution

This bug can be fixed by adding the popular USD surrogates to the list of symbols.. TUSD, USDC, GUSD, HUSD.

Your Environment

// Run kelp version to get the version and build information and paste it here
// version: v1.0.0-rc1
// git hash: 1bcc4e9
// build date: 20180813T013016Z
// GOOS: linux
// GOARCH: amd64

...

Context

USDT prices are inflated because USDT is so flakey. So it's imposssible to get a real USD price quote unless you use USDC, but you can't because the bot crashes. please add these symbols to the ccxt table

Attachments

// Attach any relevant configuration files, logs, tx hashes, etc. here.

[nikhilsaraf]

approved PR to add USDC #111
@skirsch / @paul-token please add any other USD tokens you'll may be interested in trading with a similar PR. thanks!

[nikhilsaraf]

closing this out. If there are any more USD tokens you want to add or any other tokens, feel free to submit a PR.