Bugfix: Babel targets value can be a String (#8268)

* Fix modern SSR build when Babel configuration uses a String value for "targets". Fixes #8255.

* Add custom babelrc integration tests

packages/next/build/babel/preset.ts

@@ -73,7 +73,11 @@ module.exports = (
   // if not explicitly specified:
   if (
     (isServer || isTest) &&
-    (!presetEnvConfig.targets || !('node' in presetEnvConfig.targets))
+    (!presetEnvConfig.targets ||
+      !(
+        typeof presetEnvConfig.targets === 'object' &&
+        'node' in presetEnvConfig.targets
+      ))
   ) {
     presetEnvConfig.targets = {
       // Targets the current process' version of Node. This requires apps be

test/integration/babel-custom/fixtures/targets-browsers/.babelrc

+{
+  "presets": [
+    [
+      "next/babel",
+      {
+        "preset-env": {
+          "targets": {
+            "browsers": "chrome>71"
+          }
+        }
+      }
+    ]
+  ]
+}
\ No newline at end of file

test/integration/babel-custom/fixtures/targets-browsers/pages/index.js

+export default () => <h1>Hello World</h1>

test/integration/babel-custom/fixtures/targets-string/.babelrc

+{
+  "presets": [
+    [
+      "next/babel",
+      {
+        "preset-env": {
+          "targets": "chrome>71"
+        }
+      }
+    ]
+  ]
+}
\ No newline at end of file

test/integration/babel-custom/fixtures/targets-string/pages/index.js

+export default () => <h1>Hello World</h1>

test/integration/babel-custom/test/.babelrc

+{
+  "presets": [
+    ["next/babel", {
+      "preset-env": {
+        "modules": "commonjs"
+      }
+    }]
+  ]
+}
\ No newline at end of file

test/integration/babel-custom/test/index.test.js

+/* eslint-env jest */
+/* global jasmine */
+import { join } from 'path'
+import { nextBuild } from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 5
+
+describe('Babel', () => {
+  it('should allow setting targets.browsers', async () => {
+    await nextBuild(join(__dirname, '../fixtures/targets-browsers'))
+  })
+
+  it('should allow setting targets to a string', async () => {
+    await nextBuild(join(__dirname, '../fixtures/targets-string'))
+  })
+})