Fixed typo in documentation

lib/api/graph.js

@@ -18,7 +18,7 @@ var client = require("../client");
  *  dogapi.initialize(options);
  *  var query = "system.cpu.idle{*}";
  *  var to = dogapi.now();
- *  var from = from - 3600;  // an hour ago
+ *  var from = to - 3600;  // an hour ago
  *  dogapi.graph.snapshot(query, from, to, function(err, res){
  *    console.dir(res);
  *  });