add webp support for typescript

Author: dugagjin

packages/react-scripts/lib/react-app.d.ts

@@ -43,6 +43,11 @@ declare module '*.svg' {
   export default src;
 }
 
+declare module '*.webp' {
+    const src: string;
+    export default src;
+}
+
 declare module '*.module.css' {
   const classes: { [key: string]: string };
   export default classes;