fix(warnings): remove lifecycle warnings. (react-bootstrap#4244)

Read https://reactjs.org/blog/2019/08/08/react-v16.9.0.html#renaming-unsafe-lifecycle-methods for more details

Author: patelnav

src/Carousel.js

@@ -99,7 +99,7 @@ class Carousel extends React.Component {
     this.waitForNext();
   }
 
-  componentWillReceiveProps(nextProps) {
+  UNSAFE_componentWillReceiveProps(nextProps) { // eslint-disable-line
     const activeIndex = this.getActiveIndex();
 
     if (

src/CarouselItem.js

@@ -32,7 +32,7 @@ class CarouselItem extends React.Component {
     this.isUnmounted = false;
   }
 
-  componentWillReceiveProps(nextProps) {
+  UNSAFE_componentWillReceiveProps(nextProps) { // eslint-disable-line
     if (this.props.active !== nextProps.active) {
       this.setState({ direction: null });
     }

src/Dropdown.js

@@ -132,7 +132,7 @@ class Dropdown extends React.Component {
     this.focusNextOnOpen();
   }
 
-  componentWillUpdate(nextProps) {
+  UNSAFE_componentWillUpdate(nextProps) { // eslint-disable-line
     if (!nextProps.open && this.props.open) {
       this._focusInDropdown = contains(
         ReactDOM.findDOMNode(this.menu),

src/TabContent.js

@@ -97,7 +97,7 @@ class TabContent extends React.Component {
     };
   }
 
-  componentWillReceiveProps(nextProps) {
+  UNSAFE_componentWillReceiveProps(nextProps) { // eslint-disable-line
     if (!nextProps.animation && this.state.activeChild) {
       this.setState({ activeKey: null, activeChild: null });
     }

src/utils/deprecationWarning.js

@@ -25,11 +25,11 @@ function deprecationWarning(oldname, newname, link) {
 
 deprecationWarning.wrapper = (Component, ...args) =>
   class DeprecatedComponent extends Component {
-    componentWillMount(...methodArgs) {
+    UNSAFE_componentWillMount(...methodArgs) {  // eslint-disable-line
       deprecationWarning(...args);
 
-      if (super.componentWillMount) {
-        super.componentWillMount(...methodArgs);
+      if (super.UNSAFE_componentWillMount) {
+        super.UNSAFE_componentWillMount(...methodArgs);
       }
     }
   };