Fix SecureString package

For some reason the newer package was removed from the feeds.

Microsoft.PowerShell.Linux.Host/project.json

@@ -7,7 +7,6 @@
     "licenseUrl": "",
 
     "dependencies": {
-        "Microsoft.Extensions.PlatformAbstractions": "1.0.0-*",
         "System.Management.Automation": "",
         "Microsoft.PowerShell.Security": "",
         "Microsoft.PowerShell.Commands.Utility": "",
@@ -21,6 +20,7 @@
     "frameworks": {
         "dnxcore50": {
             "dependencies": {
+		"Microsoft.Extensions.PlatformAbstractions": "1.0.0-*",
                 "System.Console": "4.0.0-beta-23420",
                 "Microsoft.CSharp": "4.0.1-beta-23420",
                 "System.Collections": "4.0.11-beta-23420",