fix(Carousel): ie11 compatibility changes(reactstrap#1571)

This applies the CustomEvent polyfill recommended in the [MDN web
docs](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent#Polyfill). This also applies a simple polyfill I found in the (react-transition-group module)[https://github.com/reactjs/react-transition-group/blob/9e3b2d3c09b78e755bdc837b7b38337812ede2c9/src/TransitionGroup.js#L11].

I don't think this has much potential to break anything, since these
will only impact browswers where these features are already broken.

src/index.js

@@ -85,3 +85,4 @@ export UncontrolledDropdown from './UncontrolledDropdown';
 export UncontrolledTooltip from './UncontrolledTooltip';
 export Spinner from './Spinner';
 export * as Util from './utils';
+export * as Polyfill from './polyfill'

src/polyfill.js

@@ -0,0 +1,20 @@
+(() => {
+  if ( typeof window.CustomEvent === 'function' ) return;
+
+  const CustomEvent = (( event, params ) => {
+    params = params || { bubbles: false, cancelable: false, detail: null };
+    var evt = document.createEvent( 'CustomEvent' );
+    evt.initCustomEvent( event, params.bubbles, params.cancelable, params.detail );
+    return evt;
+  });
+
+  window.CustomEvent = CustomEvent;
+})();
+
+(() => {
+  if ( typeof Object.values === 'function' ) return;
+
+  const values = ( (O) => Object.keys(O).map((key) => O[key]) );
+
+  Object.values = values;
+})();