Revert back to Mono capable version of Nunit

Author: Cory Thompson

test/WebPush.Test.csproj

@@ -50,8 +50,8 @@
     <Reference Include="Microsoft.Threading.Tasks.Extensions.Desktop, Version=1.0.168.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
       <HintPath>..\packages\Microsoft.Bcl.Async.1.0.168\lib\net40\Microsoft.Threading.Tasks.Extensions.Desktop.dll</HintPath>
     </Reference>
-    <Reference Include="nunit.framework, Version=3.6.1.0, Culture=neutral, PublicKeyToken=2638cd05610744eb, processorArchitecture=MSIL">
-      <HintPath>..\packages\NUnit.3.6.1\lib\net40\nunit.framework.dll</HintPath>
+    <Reference Include="nunit.framework, Version=2.6.4.14350, Culture=neutral, PublicKeyToken=96d09a1eb7f44a77, processorArchitecture=MSIL">
+      <HintPath>..\packages\NUnit.2.6.4\lib\nunit.framework.dll</HintPath>
     </Reference>
     <Reference Include="System" />
     <Reference Include="System.IO, Version=2.6.10.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">

test/packages.config

@@ -5,5 +5,5 @@
   <package id="Microsoft.Bcl.Async" version="1.0.168" targetFramework="net40" />
   <package id="Microsoft.Bcl.Build" version="1.0.21" targetFramework="net40" />
   <package id="Microsoft.Net.Http" version="2.2.29" targetFramework="net40" />
-  <package id="NUnit" version="3.6.1" targetFramework="net40" />
+  <package id="NUnit" version="2.6.4" targetFramework="net40" />
 </packages>