Fix appveyor yaml.
Fix appveyor yaml.

* Remove the install step for dependencies as build step installs too.
* Build in a separate directory rather than a directory within sources.
opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core