修复参加比赛的错误

hydro/lib/rank.js

@@ -0,0 +1,11 @@
+module.exports = function* ranked(diter, equ = (a, b) => a == b) {
+    let last_doc = null;
+    let r = 0, count = 0;
+    for (let doc of diter) {
+        count++;
+        if (count == 1 || !equ(last_doc, doc))
+            r = count;
+        last_doc = doc;
+        yield [r, doc];
+    }
+};