Fix the upgradeProxy tasks to be compatible with Linux

[jatZama]

We noticed formatting error for the newImplem and currentImplem variables on Linux machine when doing the upgrade of GatewayContract with @stongo today. We had to manually append :GatewayContract to both of those, otherwise the upgrade task would fail.

[stongo]

@jatZama is there an update on this? we will be redeploying the coproc smart contracts for StableTestnet soon, and I anticipate contract upgrades will be required this quarter.

[jatZama]

@stongo I redid the whole deployment + verification + upgrade flow on a linux VM running in AWS today and I was unable to reproduce the bug dicsussed in this issue. The upgrade worked seamlessly from first try, without changing anything from the upgrade task.
Note however that I used the new deployment flow which does not rely on the initial nonce of the deployer anymore, from this PR: #233
Maybe we should close this issue then?

[immortal-tofu]

Let's close it, we'll reopen it if we encounter the issue again.