updating devcontainers

Author: LukasAud

.devcontainer/Dockerfile

@@ -1,7 +1,7 @@
 # See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.154.2/containers/ruby/.devcontainer/base.Dockerfile
 
 # [Choice] Ruby version: 2, 2.7, 2.6, 2.5
-ARG VARIANT="2.7"
+ARG VARIANT="3.1"
 FROM mcr.microsoft.com/vscode/devcontainers/ruby:0-${VARIANT}
 
 # [Option] Install Node.js

.devcontainer/devcontainer.json

@@ -6,7 +6,7 @@
     "dockerfile": "Dockerfile",
     "args": {
       // Update 'VARIANT' to pick a Ruby version: 2, 2.7, 2.6, 2.5
-      "VARIANT": "2.5",
+      "VARIANT": "3.1",
       // Options
       "INSTALL_NODE": "false",
       "NODE_VERSION": "lts/*"