allow key to be string or number

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-datalist-input",
-  "version": "1.1.27",
+  "version": "1.1.28",
   "description": "This package provides a react component as follows: an input field with a drop down menu to pick a possible option based on the current input.",
   "main": "./lib/DataListInput.js",
   "license": "MIT",

src/DataListInput.jsx

@@ -297,7 +297,10 @@ DataListInput.propTypes = {
     items: PropTypes.arrayOf(
         PropTypes.shape( {
             label: PropTypes.string.isRequired,
-            key: PropTypes.number.isRequired,
+            key: PropTypes.oneOfType(
+                PropTypes.string,
+                PropTypes.number,
+            ).isRequired,
         } ),
     ).isRequired,
     placeholder: PropTypes.string,