Resolve #38 - Bump compatibility to "less than v13.0.0" for Newtonsoft JSON

I have tested v12.0.1 and it works just fine with this library, so I can
declare support for anything lower than the next breaking change.

Author: craigfowler

CSF.WebDriverExtras/CSF.WebDriverExtras.nuspec

@@ -12,7 +12,7 @@
     <copyright>Copyright 2017</copyright>
     <dependencies>
       <dependency id="CSF.Configuration" version="[1.1.2,2.0.0)" />
-      <dependency id="Newtonsoft.Json" version="[10.0.3,11.0.0)" />
+      <dependency id="Newtonsoft.Json" version="[10.0.3,13.0.0)" />
       <dependency id="Selenium.WebDriver" version="[3.4.0,4.0.0)" />
     </dependencies>
   </metadata>