update petridish@2.5.0 to helix-simulator@2.6.1

[tripodsan]

the PR in #314 was never run on circleci.
maybe because it originated from a forked repo?

@stefan-guggisberg I created a new PR in #318. can you have a look why it fails on circleci ?

@trieloff do you know why circleci doesn't run jobs for PRs for forked repos?

[stefan-guggisberg]

the reason why it works on git-server and helix-simulator circleci builds but fails on helix-cli is the different docker image versions being used. helix-cli uses circleci/node:8-stretch (debian 9) whereas the others are using circleci/node:8 (debian 8).

i've found similar issues related to openssl on debian 9 vs debian 8.