Allow empty width/height (#61)

Co-authored-by: Sean Willis <sean.willis@incorta.com>

Author: swillis12

types/NewWindow.d.ts

@@ -11,8 +11,8 @@ declare module 'react-new-window' {
    * @remarks These will be concatenated into a string for window.open.
    */
   export interface IWindowFeatures {
-    height: number
-    width: number
+    height?: number
+    width?: number
     [i: string]: boolean | number | string
   }