feat: add missing proptypes

Author: hudovisk

src/Experiment.js

@@ -1,11 +1,18 @@
 import React from "react";
+import PropTypes from "prop-types";
 import OptimizeContext from "./OptimizeContext";
 
 class Experiment extends React.Component {
   static defaultProps = {
     loader: null
   };
 
+  static propTypes = {
+    id: PropTypes.string.isRequired,
+    loader: PropTypes.node,
+    children: PropTypes.node
+  };
+
   state = {
     variant: null
   };

src/Variant.js

@@ -1,7 +1,13 @@
 import React from "react";
+import PropTypes from "prop-types";
 import OptimizeContext from "./OptimizeContext";
 
 class Variant extends React.Component {
+  static propTypes = {
+    id: PropTypes.string.isRequired,
+    children: PropTypes.node
+  };
+
   render() {
     return (
       <OptimizeContext.Consumer>