fix invalid JSON in devcontainer.json example (#376)

trailing comma is not allowed in JSON (although VSCode can tolerate it)

Author: tayloraswift

docs/remote-dev.md

@@ -21,7 +21,7 @@ First create the directory. Next, create `devcontainer.json` and insert the foll
     "name": "Swift 5.5",
     "image": "swift:5.5",
     "extensions": [
-      "sswg.swift-lang",
+      "sswg.swift-lang"
     ],
     "settings": {
       "lldb.library": "/usr/lib/liblldb.so"
@@ -113,4 +113,4 @@ VSCode allows you to automatically configure your project with a dev container.
 
 Once you've set up your `.devcontainer`, in the command palette run **Remote-Containers: Reopen in Container**. VSCode will relaunch running in your remote container!
 
-For more details about running your project in a remote container, and the available configuration options, see the [Visual Studio Code documentation](https://code.visualstudio.com/docs/remote/remote-overview).
+For more details about running your project in a remote container, and the available configuration options, see the [Visual Studio Code documentation](https://code.visualstudio.com/docs/remote/remote-overview).