Meta: Update GitHub links to use tc39 organization (#12)

Author: gibson042

README.md

@@ -14,7 +14,7 @@ A TC39 proposal for immutable ArrayBuffers.
 - Richard Gibson (@gibson042)
 - Jack-Works (@Jack-Works)
 
-**Specification**: https://papers.agoric.com/tc39-proposal-immutable-arraybuffer/
+**Specification**: https://tc39.es/tc39-proposal-immutable-arraybuffer/
 
 ## Presentation history
 

spec.emu

@@ -7,7 +7,7 @@
 title: Immutable ArrayBuffers
 status: proposal
 stage: 0
-shortname: <a href="https://github.com/Agoric/tc39-proposal-immutable-arraybuffer">proposal-immutable-arraybuffer</a>
+shortname: <a href="https://github.com/tc39/tc39-proposal-immutable-arraybuffer">proposal-immutable-arraybuffer</a>
 contributors: Mark S. Miller, Richard Gibson
 </pre>