Update react.d.ts

Having context as {} did not allow me access context members via .notation.

react/react.d.ts

@@ -173,7 +173,7 @@ declare namespace __React {
         // on the existence of `children` in `P`, then we should remove this.
         props: P & { children?: ReactNode };
         state: S;
-        context: {};
+        context: any;
         refs: {
             [key: string]: ReactInstance
         };