Update package version to 3.1.0-beta

Author: marcin-golebiowski

src/SpiceSharpParser/SpiceSharpParser.csproj

@@ -22,7 +22,7 @@
     <StartupObject />
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <LangVersion>latest</LangVersion>
-    <Version>3.1.0-alfa</Version>
+    <Version>3.1.0-beta</Version>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|netstandard1.5|AnyCPU'">