Define TypeScript compiler target (#522)

TypeScript was complaining about some syntax features, this solves it.
It doesn’t affect the output, as `tsdx` ignores the `target` property.

Author: remcohaszing

packages/tailwindcss-language-service/tsconfig.json

@@ -3,6 +3,7 @@
   "compilerOptions": {
     "module": "esnext",
     "lib": ["ES2020"],
+    "target": "ES2020",
     "importHelpers": true,
     "declaration": true,
     "sourceMap": true,