Adapt the way to connect mimcs

src/mimc7.js

@@ -44,10 +44,21 @@ exports.hash =  (_x_in, _k) =>{
     return F.affine(F.add(r, k));
 };
 
-exports.multiHash = (arr) => {
-    let r = exports.getIV();
-    for (let i=0; i<arr.length; i++) {
-        r = exports.hash(r, bigInt(arr[i]));
+exports.multiHash = (arr, key) => {
+    let r;
+    if (typeof(key) === "undefined") {
+        r = F.zero;
+    } else {
+        r = key;
     }
-    return r;
+    for (let i=0; i<arr.length; i++) {
+        r = F.add(
+            F.add(
+                r,
+                arr[i]
+            ),
+            exports.hash(bigInt(arr[i]), r)
+        );
+    }
+    return F.affine(r);
 };