Align all babel-preset-xxx packages dir structures with status quo

packages/babel-preset-es2016/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-es2016",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-transform-exponentiation-operator": "^6.3.13"
   }

packages/babel-preset-es2017/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-es2017",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-syntax-trailing-function-commas": "^6.8.0",
     "babel-plugin-transform-async-to-generator": "^6.8.0"

packages/babel-preset-react/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-react",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-syntax-flow": "^6.3.13",
     "babel-plugin-syntax-jsx": "^6.3.13",

packages/babel-preset-stage-0/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-stage-0",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-transform-do-expressions": "^6.3.13",
     "babel-plugin-transform-function-bind": "^6.3.13",

packages/babel-preset-stage-1/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-stage-1",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-transform-class-constructor-call": "^6.3.13",
     "babel-plugin-transform-export-extensions": "^6.3.13",

packages/babel-preset-stage-2/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-stage-2",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-transform-class-properties": "^6.3.13",
     "babel-plugin-transform-decorators": "^6.13.0",

packages/babel-preset-stage-3/package.json

@@ -6,7 +6,7 @@
   "homepage": "https://babeljs.io/",
   "license": "MIT",
   "repository": "https://github.com/babel/babel/tree/master/packages/babel-preset-stage-3",
-  "main": "index.js",
+  "main": "lib/index.js",
   "dependencies": {
     "babel-plugin-syntax-trailing-function-commas": "^6.3.13",
     "babel-plugin-transform-async-to-generator": "^6.3.13",