Fix Newtonsoft.Json Pester tests

Look for library in new location.

src/Microsoft.PowerShell.Linux.Host/project.json

@@ -9,6 +9,7 @@
 
     "dependencies": {
 	"NETStandard.Library": "1.0.0-rc2-23616",
+	"Newtonsoft.Json": "8.0.1-beta3",
         "Microsoft.PowerShell.Commands.Utility": {
 	    "type": "build",
 	    "version": "1.0.0-*"

src/pester-tests/Json.Tests.ps1

@@ -8,7 +8,7 @@ $here = Split-Path -Parent $MyInvocation.MyCommand.Path
 
 Describe "Json.NET LINQ Parsing" {
     # load third party Json.NET library
-    $path = "tools/Newtonsoft.Json.7.0.1/lib/portable-net45+wp80+win8+wpa81+dnxcore50/Newtonsoft.Json.dll"
+    $path = "$env:CORE_ROOT/Newtonsoft.Json.dll"
     [Microsoft.PowerShell.CoreCLR.AssemblyExtensions]::LoadFrom($path)
 
     BeforeEach {