Use latest packer 0.12.2

Signed-off-by: Stefan Scherer <scherer_stefan@icloud.com>

README.md

@@ -14,7 +14,7 @@ Some of my enhancements are:
 
 ### Packer Version
 
-[Packer](https://github.com/mitchellh/packer/blob/master/CHANGELOG.md) `0.10.0` or greater is required.
+[Packer](https://github.com/mitchellh/packer/blob/master/CHANGELOG.md) `0.12.2` or greater is required.
 
 ### Windows Versions
 

hyperv/scripts/install-packer.ps1

-choco install -y packer -version 0.12.1
+choco install -y packer