Transition to netstandard.

- dotnet5.X => netstandard1.y (where y = x-1).
- DNXCore50 => netstandardapp1.5.
- Applied the same changes to ifdefs.

src/Microsoft.AspNetCore.Session/project.json

@@ -15,15 +15,20 @@
     "allowUnsafe": true,
     "warningsAsErrors": true,
     "keyFile": "../../tools/Key.snk",
-    "nowarn": [ "CS1591" ],
+    "nowarn": [
+      "CS1591"
+    ],
     "xmlDoc": true
   },
   "frameworks": {
     "net451": {},
-    "dotnet5.4": {
+    "netstandard1.3": {
       "dependencies": {
         "System.Security.Cryptography.Algorithms": "4.0.0-*"
-      }
+      },
+      "imports": [
+        "dotnet5.4"
+      ]
     }
   }
-}
+}

test/Microsoft.AspNetCore.Session.Tests/project.json

@@ -9,12 +9,15 @@
   },
   "testRunner": "xunit",
   "frameworks": {
-    "dnxcore50": {
+    "netstandardapp1.5": {
       "dependencies": {
         "dotnet-test-xunit": "1.0.0-dev-*",
         "Microsoft.NETCore.Platforms": "1.0.1-*"
       },
-      "imports": "portable-net451+win8"
+      "imports": [
+        "dnxcore50",
+        "portable-net451+win8"
+      ]
     },
     "net451": {
       "frameworkAssemblies": {