Bump github.com/apple/swift-docc-plugin from 1.3.0 to 1.4.0

Bumps [github.com/apple/swift-docc-plugin](https://github.com/apple/swift-docc-plugin) from 1.3.0 to 1.4.0.
- [Release notes](https://github.com/apple/swift-docc-plugin/releases)
- [Commits](swiftlang/swift-docc-plugin@1.3.0...1.4.0)

---
updated-dependencies:
- dependency-name: github.com/apple/swift-docc-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Package.resolved

@@ -1,25 +1,23 @@
 {
-  "object": {
-    "pins": [
-      {
-        "package": "SwiftDocCPlugin",
-        "repositoryURL": "https://github.com/apple/swift-docc-plugin",
-        "state": {
-          "branch": null,
-          "revision": "26ac5758409154cc448d7ab82389c520fa8a8247",
-          "version": "1.3.0"
-        }
-      },
-      {
-        "package": "SymbolKit",
-        "repositoryURL": "https://github.com/apple/swift-docc-symbolkit",
-        "state": {
-          "branch": null,
-          "revision": "b45d1f2ed151d057b54504d653e0da5552844e34",
-          "version": "1.0.0"
-        }
+  "pins" : [
+    {
+      "identity" : "swift-docc-plugin",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/apple/swift-docc-plugin",
+      "state" : {
+        "revision" : "a255bbdb5d10d36788a39f239d7d2ac2734cef35",
+        "version" : "1.4.0"
       }
-    ]
-  },
-  "version": 1
+    },
+    {
+      "identity" : "swift-docc-symbolkit",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/swiftlang/swift-docc-symbolkit",
+      "state" : {
+        "revision" : "b45d1f2ed151d057b54504d653e0da5552844e34",
+        "version" : "1.0.0"
+      }
+    }
+  ],
+  "version" : 2
 }