Fix reference to mscorlib

Author: josesimoes

System.Device.I2c/System.Device.I2c.nfproj

@@ -59,6 +59,7 @@
     <Reference Include="mscorlib, Version=1.10.5.0, Culture=neutral, PublicKeyToken=c07d481e9758c731">
       <HintPath>..\packages\nanoFramework.CoreLibrary.1.10.5-preview.18\lib\mscorlib.dll</HintPath>
       <Private>True</Private>
+      <SpecificVersion>True</SpecificVersion>
     </Reference>
   </ItemGroup>
   <Import Project="$(NanoFrameworkProjectSystemPath)NFProjectSystem.CSharp.targets" Condition="Exists('$(NanoFrameworkProjectSystemPath)NFProjectSystem.CSharp.targets')" />