build: Update Node.js to v20 (#395)

.nvmrc

@@ -1 +1 @@
-18
+20

azure-pipelines.yml

@@ -48,9 +48,9 @@ extends:
                   verbosity: "Verbose"
                   alertWarningLevel: "High"
               - task: UseNode@1
-                displayName: Use Node 18.x
+                displayName: Use Node 20.x
                 inputs:
-                  version: 18.x
+                  version: 20.x
               - task: Npm@1
                 displayName: Install
                 inputs: