Updates hot property in Module interface to optional

types/webpack-env/index.d.ts

@@ -1,6 +1,7 @@
 // Type definitions for webpack (module API) 1.13
 // Project: https://github.com/webpack/webpack
 // Definitions by: use-strict <https://github.com/use-strict>
+//                 rhonsby <https://github.com/rhonsby>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 /**
@@ -60,7 +61,7 @@ declare namespace __WebpackModuleApi {
         loaded: boolean;
         parent: any;
         children: any[];
-        hot: Hot;
+        hot?: Hot;
     }
     type ModuleId = string|number;