Shashlik improved fiber radius

Small change: Reduced radius of shashlik readout fibers from 0.8mm to 0.6mm. Only files changing:
- Geometry/HGCalCommonData/data/shashlikmodule.xml 
- Geometry/HGCalCommonData/data/NoTaper/shashlikmodule.xml
...with no impact on module numbering/DetID/channel counting.

This change is important for shashlik TP studies as it provides a more realistic fiber scenario.