Corrects error in the invoice builder introduced with taxation changes.
Merge branch '1.3.0' of https://github.com/rustyswayne/Merchello into 1.3.0

Conflicts:
	build/Merchello.Version.props
	build/NuSpec/Merchello.Core.nuspec
	src/Merchello.Core/Configuration/MerchelloVersion.cs
	src/Merchello.Core/Properties/AssemblyInfo.cs
	src/Merchello.Web/Properties/AssemblyInfo.cs