change the way the google key is stored

[12rambau]

At the moment the google json key is transformed into a env_var and send to the different services that require an access to this information.

Problem : RDT only accept a 2048 character env var and the json key end up being 3048 character long.

I opened an issue on their repository (readthedocs/readthedocs.org#7901) and it doesn't seems that they will change their env variable behaviour.
On the other hand we can change the decoding behaviour:
crypting the json file in the lib using a salt that I will use as a env variable to decode in codeCov, codeClimate, Travis and RDT the json file.

[12rambau]

I've also updated the keys in travis and RDT