appveyor.yml: change versioning to '{branch}.{build}' format
appveyor.yml: change versioning to '{branch}.{build}' format

The old '2015.1.{build}' format is a bit confusing, because it gives the
impression that something is stuck in the past.

Change this to '{branch}.{build}'.
That way we don't need to care about date/time, since Appveyor will track
that anyway.

Signed-off-by: Alexandru Ardelean <685557f6b7c225d86b536740313ed51b24843a58@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio