fix: handle process.version set to undefined (#78) (#80)

Vercel's [Edge Runtime](https://edge-runtime.vercel.app/) is not Node.js, but will have a global `process` defined

Co-authored-by: Jascha Ephraim <jaschaephraim@gmail.com>

src/index.ts

@@ -3,7 +3,7 @@ export function getUserAgent(): string {
     return navigator.userAgent;
   }
 
-  if (typeof process === "object" && "version" in process) {
+  if (typeof process === "object" && process.version !== undefined) {
     return `Node.js/${process.version.substr(1)} (${process.platform}; ${
       process.arch
     })`;