Fix coverage result response reading

[killy971]

The following change was introduced on codecov server side, apparently by codecov/codecov-python@2eab8f9: instead of containing the total coverage result as a value, the response to codecov initial post request now contains a url (wait_url element in the json content).
Reading this url should return the coverage result in json format as in the example below:

{"coverage": 42}

Here is the code showing how codecov-python implements the functionality to wait and read the total coverage result.

[killy971]

The logic should be easy to implement in a similar to what was done to read and parse the page linked from coveralls response (See killy971/hpc-coveralls#21).

[stevepeak]

I did a poor job of announcing this change. Thanks @guillaume-nargeot for recognizing this.

[killy971]

No problem Steve!

I've just fixed the problem, and will add retry logic later.

[killy971]

Feature branch: https://github.com/guillaume-nargeot/codecov-haskell/tree/fix-coverage-response-reading
Fixed by 078bca0

[killy971]

Another change was required to fix the problem: using the CurlFollowLocation option in order to follow the link returned by HTTP 301 responses.
This issue is now fixed as of 1c623d5