Make a test in case multiple bids have the same maximum valuation, the last ones have the priority

[stefek99]

See the commit updating readme: https://github.com/kleros/openiico-contract/commit/e4862822d9e0ac7d0985f24dc701dbcd567a7ee2

It's counterintuitive at first, and then:

• can set valuatoin 1 wei higher
• will have lower bonus

Is starting to make sense