Merge pull request #10 from JSkimming/target-dotnet451

Target .NET 4.5.1 as well as .NET Standard 1.6

Author: nbarbettini

src/Stormpath.AspNetCore/project.json

@@ -21,6 +21,7 @@
   },
   "description": "Stormpath middleware for ASP.NET Core. Easily adds authentication and authorization to ASP.NET Core applications.",
   "frameworks": {
+    "net451": {},
     "netstandard1.6": {
       "imports": "dotnet"
     }