fix seperators typo (#7932)

Its the little things that makes the big difference!  😁

Thanks

Author: donavon

packages/babel-preset-react-app/create.js

@@ -154,7 +154,7 @@ module.exports = function(api, opts, env) {
           loose: true,
         },
       ],
-      // Adds Numeric Seperators
+      // Adds Numeric Separators
       require('@babel/plugin-proposal-numeric-separator').default,
       // The following two plugins use Object.assign directly, instead of Babel's
       // extends helper. Note that this assumes `Object.assign` is available.