Add missing module declaration after namespace

This was inadvertently removed in 5bc6d65.

This time, I have double checked that the declaration is functional from TypeScript. Sorry about the mix-up!

Author: François Wouts

src/jsgraphs.d.ts

@@ -250,3 +250,7 @@ declare namespace JsGraphs {
         minCut(G: FlowNetwork): FlowEdge[];
     }
 }
+
+declare module "js-graph-algorithms" {
+  export = JsGraphs;
+}