Avoid requests to external resources from tests

[kaero]

https://travis-ci.org/nodules/asker/builds/43318134
https://travis-ci.org/nodules/asker/builds/43318136

[narqo]

Encoders part was fixed with #112.

[kaero]

@narqo had you observe flaky results of tests in last time?

[kaero]

@narqo ping

[narqo]

No, but as we request an external resources in our https tests (e.g. https://yandex.com), I don't see a reason it to stay 100% stable.