update v8 version in readme to match reality
## A secure TypeScript runtime built on V8
-* Supports TypeScript 2.8 out of the box. Uses V8 6.8.275.3. That is, it's
+* Supports TypeScript 2.8 out of the box. Uses V8 6.9.297. That is, it's
very modern JavaScript.
* No `package.json`. No npm. Not explicitly compatible with Node.
