commit yarn.lock for deterministic builds

[dreamalligator]

it is good practice to commit your yarn.lock file for deterministic builds.

see https://yarnpkg.com/lang/en/docs/yarn-lock/

hacktoberfest

[vmarkovtsev]

Hi @nebulousdog, we are waiting for our blog technical maintainer, @dpordomingo, to return from the paternity leave. Once he gets back to work he will certainly review this! Stay tuned and thanks for your contribution.

[dpordomingo]

Hi, the yarn.lock file is already there https://github.com/src-d/blog/blob/master/yarn.lock

Feel free to reopen in case you want to improve the build with new features

[dreamalligator]

thanks! missed that.