Fix VersionedMap deserialization issue

Resolves #334.

lib/versioned-map.js

@@ -127,15 +127,15 @@ class VersionedMap {
 
   setRevisions(key, revisionsObj) {
     const del = revisionsObj.delete || 0;
-    const maxRev = Object.keys(revisionsObj).reduce(
+    const mutations = Object.keys(revisionsObj).reduce(
-      (acc, cur) => (+cur > acc ? +cur : acc),
+      (acc, cur) => (cur === "delete" ? acc : acc | (1 << +cur)),
-      0
+      del
     );
 
     const revisions = [];
 
     let prev = NONEXISTENT;
-    for (let i = 0; i <= maxRev; ++i) {
+    for (let i = 0; mutations >> i; ++i) {
       let v = prev;
       if (del & (1 << i)) v = NONEXISTENT;
       else if (i in revisionsObj) v = revisionsObj[i];