Merge pull request #142 from konklone/patch-2

Grammar fix

doc/index.md

@@ -67,7 +67,7 @@ Glad you asked!
   order of magnitude or more.  In fact, usually it's no more than some inline accessor methods!
 * **Tiny runtime library:** Due to the simplicity of the Cap'n Proto format, the runtime library
   can be much smaller.
-* **Time-traveling RPC:** Cap'n Proto features an RPC system implements [time travel](rpc.html)
+* **Time-traveling RPC:** Cap'n Proto features an RPC system that implements [time travel](rpc.html)
   such that call results are returned to the client before the request even arrives at the server!
 
 <a href="rpc.html"><img src='images/time-travel.png' style='max-width:639px'></a>