SmallSharp should be a development dependency

Fixes #95

Author: kzu

src/SmallSharp/SmallSharp.csproj

@@ -7,6 +7,7 @@
     <PackFolder>build\netstandard2.0</PackFolder>
     <PackNone>true</PackNone>
     <GenerateDocumentationFile>false</GenerateDocumentationFile>
+    <DevelopmentDependency>true</DevelopmentDependency>
   </PropertyGroup>
 
   <ItemGroup>
@@ -30,4 +31,4 @@
     <UpToDateCheckInput Include="SmallSharp.targets" />
   </ItemGroup>
 
-</Project>
+</Project>