API version v1 is default even though documentation claims v2 is default

[ryandgoulding]

Documentation: https://github.com/tiaanduplessis/coinmarketcap-api/blob/master/index.js#L13

v.s.

Code: https://github.com/tiaanduplessis/coinmarketcap-api/blob/master/index.js#L18

I don't really care which is default, but the code and docs should be consistent at the least.