Remove element at once when transitonLeave is false

Previously transitionLeave being false did not affect the behavior and
in dom the old component still existed together with the new component.

This does not show old component at all when new component is ready to
be rendered.

Author: wifilinker

src/ReactCSSTransitionReplace.jsx

@@ -133,7 +133,7 @@ export default class ReactCSSTransitionReplace extends React.Component {
     if (!this.isTransitioning && !this.state.isLeaving) {
       const {currentChild, nextChild } = this.state
 
-      if (currentChild && (nextChild || nextChild === false || nextChild === null)) {
+      if (currentChild && (nextChild || nextChild === false || nextChild === null) && this.props.transitionLeave) {
         this.leaveCurrent()
       }
       if (nextChild) {
@@ -263,7 +263,7 @@ export default class ReactCSSTransitionReplace extends React.Component {
       ...containerProps,
     } = this.props
 
-    if (currentChild) {
+    if (currentChild && !nextChild && !transitionLeave || currentChild && transitionLeave) {
       childrenToRender.push(
         React.createElement(
           'span',