migrate index.js to typescript (reduxjs#3513)

Former-commit-id: 86253da

Author: cellog

rollup.config.js

@@ -9,7 +9,7 @@ import pkg from './package.json'
 export default [
   // CommonJS
   {
-    input: 'src/index.js',
+    input: 'src/index.ts',
     output: { file: 'lib/redux.js', format: 'cjs', indent: false },
     external: [
       ...Object.keys(pkg.dependencies || {}),
@@ -24,7 +24,7 @@ export default [
 
   // ES
   {
-    input: 'src/index.js',
+    input: 'src/index.ts',
     output: { file: 'es/redux.js', format: 'es', indent: false },
     external: [
       ...Object.keys(pkg.dependencies || {}),
@@ -39,7 +39,7 @@ export default [
 
   // ES for Browsers
   {
-    input: 'src/index.js',
+    input: 'src/index.ts',
     output: { file: 'es/redux.mjs', format: 'es', indent: false },
     plugins: [
       nodeResolve(),
@@ -63,7 +63,7 @@ export default [
 
   // UMD Development
   {
-    input: 'src/index.js',
+    input: 'src/index.ts',
     output: {
       file: 'dist/redux.js',
       format: 'umd',
@@ -84,7 +84,7 @@ export default [
 
   // UMD Production
   {
-    input: 'src/index.js',
+    input: 'src/index.ts',
     output: {
       file: 'dist/redux.min.js',
       format: 'umd',