Update to go-1.13

[carlosms]

Go 1.13 is out, according to our conventions we should update.

[dpordomingo]

Do we want to use go1.13 error wrapping instead of current go-error?
Should we confirm it company-wide?

[carlosms]

I would say yes, but it's something we can do later. Maybe we can open a new issue to src-d/guide to discuss it (as the convention is documented here https://github.com/src-d/guide/blob/master/engineering/conventions/go.md#error-handling)

[dpordomingo]

I would say yes, but it's something we can do later. Maybe we can open a new issue to src-d/guide to discuss it (as the convention is documented here https://github.com/src-d/guide/blob/master/engineering/conventions/go.md#error-handling)

Good idea. Issue opened here src-d/guide#383