Fix docker image building

[mpetrunic]

Describe the bug

Seems like dockerhub is having trouble building image.

Expected behavior

Should work every time.

Steps to Reproduce

1. trigger build on dockerhub

Screenshots

https://hub.docker.com/repository/registry-1.docker.io/chainsafe/lodestar/builds/72fd665b-e78c-41b0-935e-2c3081ec933f

Desktop (please complete the following information):

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Solution:

• try to add longer timeout to yarn in docker: There appears to be trouble with your network connection. Retrying... yarnpkg/yarn#4890 (comment)