Adding types for recurseButtons method. Per https://github.com/hodgef/react-simple-keyboard/issues/960

src/lib/components/Keyboard.js

@@ -880,7 +880,7 @@ class SimpleKeyboard {
    * Execute an operation on each button
    */
   recurseButtons(fn) {
-    if (!fn) return false;
+    if (!fn) return;
 
     Object.keys(this.buttonElements).forEach(buttonName =>
       this.buttonElements[buttonName].forEach(fn)

src/lib/components/tests/Keyboard.test.js

@@ -1376,7 +1376,7 @@ it('Keyboard buttonAttribute will warn about invalid entries', () => {
 it('Keyboard recurseButtons will not work without a valid param', () => {
   setDOM();
   const keyboard = new Keyboard();
-  expect(keyboard.recurseButtons()).toBe(false);
+  expect(keyboard.recurseButtons()).toBeFalsy();
 });
 
 it('Keyboard will not work with a DOM element param without class', () => {