Merge #580

580: update lockfile / dependencies r=mkroening a=striezel

Updating futures-core v0.3.24 -> v0.3.25
Updating getrandom v0.2.7 -> v0.2.8
Updating libc v0.2.135 -> v0.2.137
Updating ppv-lite86 v0.2.16 -> v0.2.17
Updating syn v1.0.102 -> v1.0.103

I am aware that there is a dependabot configuration for keeping such stuff up to date, but it looks like some stuff (e. g. `getrandom` or `ppv-lite`) does not get picked up by dependabot.

Co-authored-by: Dirk Stolle <striezel-dev@web.de>