[token-server] Bump XEC reward

Summary:
With rate limiting implemented (which can be adjusted further) and IP-logging corrected, better countermeasures are available if we see another sustained script on the faucet.

At the moment, the "10 xec max out every hour" guy has stopped, which makes testing this kind of thing a little trickier. Perhaps this reward will bring him back.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16709