fix compiler errors and make test pass

Tasklist:
- $5 + 10CHF = $10 if rate is 2:1 🎯
- $5 * 2 = $10 👈🏼
- Make "amount" private
- Dollar side-effects?
- Money rounding?

src/index.spec.ts

@@ -1,3 +1,5 @@
+import Dollar from '.';
+
 describe('Multi currency money', () => {
   it.todo('should sum $5 + 10CHF as being $10 if exchange rate is 2:1');
 

src/index.ts

@@ -1 +1,11 @@
-console.log('Hello world!');
+export default class Dollar {
+  amount: number;
+
+  constructor(amount: number) {
+    this.amount = amount;
+  }
+
+  times(multiplier: number) {
+    this.amount *= multiplier;
+  }
+}