chore(readme): fix typo (#36)

Co-authored-by: Joe Lee <jclee@users.noreply.github.com>

README.md

@@ -51,7 +51,7 @@ As of this writing, some major features are missing which we intend to fix short
 
 ### WARNING: `workerd` is not a hardened sandbox
 
-`workerd` tries to isolate each Worker so that it can only access the resources it is configured to access. However, `workerd` on its own does not contain suitable defense-in-depth against the possibliity of implementation bugs. When using `workerd` to run possibly-malicious code, you must run it inside an appropriate secure sandbox, such as a virtual machine. The Cloudflare Workers hosting service in particular [uses many additional layers of defense-in-depth](https://blog.cloudflare.com/mitigating-spectre-and-other-security-threats-the-cloudflare-workers-security-model/).
+`workerd` tries to isolate each Worker so that it can only access the resources it is configured to access. However, `workerd` on its own does not contain suitable defense-in-depth against the possibility of implementation bugs. When using `workerd` to run possibly-malicious code, you must run it inside an appropriate secure sandbox, such as a virtual machine. The Cloudflare Workers hosting service in particular [uses many additional layers of defense-in-depth](https://blog.cloudflare.com/mitigating-spectre-and-other-security-threats-the-cloudflare-workers-security-model/).
 
 With that said, if you discover a bug that allows malicious code to break out of `workerd`, please submit it to [Cloudflare's bug bounty program](https://hackerone.com/cloudflare?type=team) for a reward.