Extract babel config from package.json to .babelrc

Also add .babelrc to .npmignore so we don't have problems with
React-Native's packager.

Reference: reduxjs/redux#1033

.babelrc

@@ -0,0 +1,6 @@
+{
+  "presets": [
+    "es2015",
+    "stage-0"
+  ]
+}

.npmignore

@@ -1 +1,3 @@
 src
+.babelrc
+

package.json

@@ -1,6 +1,6 @@
 {
-  "name": "proptypes-schema",
-  "version": "0.0.3",
+  "name": "@nerdwallet/proptypes-schema",
+  "version": "0.0.3-rn1",
   "description": "Generic object schema modeled on React PropTypes",
   "main": "./lib/index.js",
   "scripts": {
@@ -12,18 +12,14 @@
     "clean": "rm -rf lib",
     "prepublish": "npm run build"
   },
-  "babel": {
-    "presets": [
-      "es2015",
-      "stage-0"
-    ]
-  },
   "author": "",
   "license": "MIT",
   "dependencies": {},
   "devDependencies": {
     "babel-cli": "^6.14.0",
     "babel-eslint": "^7.0.0",
+    "babel-preset-es2015": "^6.18.0",
+    "babel-preset-stage-0": "^6.16.0",
     "babel-register": "^6.16.3",
     "chai": "^3.5.0",
     "eslint": "^3.4.0",