Fix misc typos

[pieterocp]

Ended up reading through the repo since I was having issues with change_in, it was an issue on my end since I didn't realise that all jobs will run if the files change, so read through changein/function.go and nosey me sees a typo, so trawled through and addressed them.

Nothing major, just internal changes, docs improvements, error messages made clearer.

[pieterocp]

Any semaphore Devs able to give this a review?

[pieterocp]

Thanks for addressing the typo in #55, rebased with master. Any reviewers?

[hamir-suspect]

/sem-approve

[hamir-suspect]

@pieterocp would you be willing to update the Makefile as well to use the publicly available security-toolbox like here: https://github.com/semaphoreci/cli/blob/master/Makefile#L9

[pieterocp]

@pieterocp would you be willing to update the Makefile as well to use the publicly available security-toolbox like here: https://github.com/semaphoreci/cli/blob/master/Makefile#L9

@hamir-suspect no problem at all, as far as I am aware, made the changes with 81c5aec 👍