I haven’t tried this, so use caution 
Download zip from https://hudson.eclipse.org/smarthome/job/SmartHomeDistribution-Stable/
extract zip, find org.eclipse.smarthome.binding.astro_0.9.0.xyz.jar
install manually (don’t forget to uninstall the existing astro binding first)
Maybe it won’t work since there are additional changes in the ESH distro in other jars also.
Moving to snapshot is really not something to worry about. It is as stable as the release build.
You can always revert back to 2.1 stable from snapshot if you don’t like 2.2 snap 