Don't publish .babelrc file

More and more npm packages contain ES2015+ code.
As discussed in [this AMA](sindresorhus/ama#446), this causes a lot of troubles (Uglify and old browsers) for people.

One possible solution is to transpile external dependencies, as discussed in [this issue on create-react-app](facebook/create-react-app#1125) and implemented in [this pull request](facebook/create-react-app#3776).

This doesn't currently work with Webslides as the .babelrc file is published on npm.
Here is a [small repo demonstrating the bug](https://github.com/oligot/webslides-babelrc).
Running `npm run build` results in this error

```
ERROR in ./node_modules/webslides/static/js/webslides.js
Module build failed: Error: Couldn't find preset "es2015" relative to directory ".../webslides-babelrc/node_modules/webslides"
```

By adding the .babelrc file to .npmignore, and removing the babel config in the _package.json_ file, the bug would go away once a new version of Webslides is published.

This is basically the same PR as done for [v-tooltip](Akryum/floating-vue#90).

Author: oligot

.npmignore

@@ -0,0 +1 @@
+.babelrc

package.json

@@ -85,16 +85,6 @@
   "pre-commit": [
     "lint"
   ],
-  "babel": {
-    "presets": [
-      [
-        "es2015",
-        {
-          "modules": false
-        }
-      ]
-    ]
-  },
   "dependencies": {
     "request": "^2.83.0"
   }