Update tuple rule for new AST

.vscode/launch.json

@@ -1,20 +0,0 @@
-{
-    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
-    "version": "0.2.0",
-    "configurations": [
-        {
-            "type": "node",
-            "request": "attach",
-            "name": "Attach",
-            "port": 9229,
-            "sourceMaps": true
-        },
-        {
-            "type": "node",
-            "request": "launch",
-            "name": "Launch Program",
-            "program": "${workspaceRoot}/test/test.js",
-            "outFiles": ["${workspaceRoot}/bin"]
-        }
-    ]
-}

src/rules/noSingleElementTupleTypeRule.ts

@@ -21,7 +21,7 @@ export class Rule extends Lint.Rules.AbstractRule {
 function walk(ctx: Lint.WalkContext<void>): void {
     const { sourceFile } = ctx;
     sourceFile.forEachChild(function cb(node) {
-        if (ts.isTupleTypeNode(node) && node.elementTypes.length === 1) {
+        if (ts.isTupleTypeNode(node) && (node.elements ?? (node as any).elementTypes).length === 1) {
             ctx.addFailureAtNode(node, failure(
                 Rule.metadata.ruleName,
                 "Type [T] is a single-element tuple type. You probably meant T[]."));