Fix '1.2.0beta-1' is not a valid version string

Author: wallymathieu

Directory.Build.props

@@ -3,7 +3,7 @@
         <VersionPrefix>1.2.0</VersionPrefix>
         <VersionSuffix>beta-1</VersionSuffix>
         <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
-        <Version Condition=" '$(VersionSuffix)' != '' ">$(VersionPrefix)$(VersionSuffix)</Version>
+        <Version Condition=" '$(VersionSuffix)' != '' ">$(VersionPrefix)-$(VersionSuffix)</Version>
         <Version Condition=" '$(VersionSuffix)' == '' ">$(VersionPrefix)</Version>
         <AssemblyVersion>1.0.0.0</AssemblyVersion>
         <FileVersion>$(AssemblyVersion)</FileVersion>