Keep main's one-line guards where no rule needs braces

src/prepare.ts

@@ -5,9 +5,7 @@ import { prepareRuntime } from "./runtime.ts";
 
 const env = (name: string): string => {
   const value = process.env[name];
-  if (value === undefined || value === "") {
-    throw new Error(`${name} is not set`);
-  }
+  if (value === undefined || value === "") throw new Error(`${name} is not set`);
   return value;
 };