React to platform abstractions dependency addition on DotNetToolDispatcher.

Author: N. Taylor Mullen

src/Microsoft.AspNetCore.Razor.Tools/project.json

@@ -27,6 +27,7 @@
   "dependencies": {
     "Microsoft.AspNetCore.Razor.Design": "1.0.0-*",
     "Microsoft.DotNet.Cli.Utils": "1.0.0-*",
+    "Microsoft.Extensions.PlatformAbstractions": "1.0.0-*",
     "Microsoft.Extensions.DotnetToolDispatcher.Sources": {
       "type": "build",
       "version": "1.1.0-*"