Bump packages back to rc3

The primary reason to do this is that the VS Code debugger is not
compatible with rc2.

Secondarily, we want to continue tracking CoreCLR/FX master branch,
which means to continue with the latest release candidates. Since we are
releasing in August, we will be able to pick up the converged RTM
version before release.

The only advantage of rc2 is that it is frozen; but we have this anyway
because we snap to particular builds.

src/Microsoft.PowerShell.CoreCLR.AssemblyLoadContext/project.json

@@ -22,8 +22,8 @@
                 "define": [ "CORECLR" ]
             },
             "dependencies": {
-                "NETStandard.Library": "1.5.0-rc2-23922",
-                "System.Runtime.Loader": "4.0.0-rc2-23922"
+                "NETStandard.Library": "1.5.0-rc3-23922",
+                "System.Runtime.Loader": "4.0.0-rc3-23922"
             }
         }
     },