fix: Add type declaration for toBeEnabled (#80)

Author: Thomas-Ritsert

extend-expect.d.ts

@@ -8,6 +8,7 @@ declare namespace jest {
     toBeVisible(): R
     toBeEmpty(): R
     toBeDisabled(): R
+    toBeEnabled(): R
     toContainElement(element: HTMLElement | SVGElement | null): R
     toContainHTML(htmlText: string): R
     toHaveAttribute(attr: string, value?: string): R