A little bit of maintenance on the ReasonML examples (#11662)

* Add babel-types package

`next dev` was failing with:

```
Error: Cannot find module 'babel-types'
```

* Upgrade to the latest bs-platform

Also add the `babel-types` package to stop the `next dev` command from complaining.

* Remove extraneous babel-plugin-bucklescript dependency.

Seems the dependency has been deprecated, and it doesn't seem to be required
anyways.

examples/with-reasonml-todo/.babelrc

@@ -2,7 +2,4 @@
   "presets": [
     "next/babel"
   ],
-  "plugins": [
-    "babel-plugin-bucklescript"
-  ]
 }

examples/with-reasonml-todo/package.json

@@ -10,7 +10,6 @@
   },
   "license": "ISC",
   "dependencies": {
-    "babel-plugin-bucklescript": "^0.5.3",
     "next": "latest",
     "next-transpile-modules": "^3.0.2",
     "react": "^16.8.6",
@@ -19,7 +18,7 @@
   },
   "devDependencies": {
     "@babel/core": "^7.4.3",
-    "bs-platform": "5.0.3",
+    "bs-platform": "7.2.2",
     "concurrently": "^4.1.0"
   }
 }

examples/with-reasonml/.babelrc

@@ -1,8 +1,5 @@
 {
   "presets": [
     "next/babel"
-  ],
-  "plugins": [
-    "babel-plugin-bucklescript"
   ]
 }

examples/with-reasonml/package.json

@@ -10,7 +10,6 @@
   },
   "license": "ISC",
   "dependencies": {
-    "babel-plugin-bucklescript": "^0.5.3",
     "next": "latest",
     "next-transpile-modules": "^3.0.2",
     "react": "^16.12.0",