Change $unset prop values (#4)

* Changing the unset prop value for intuitive diff

* Tests are passing

Author: nigelgilbert

index.js

@@ -84,7 +84,7 @@ function set (query, field, val) {
 
 function unset (query, field) {
   query['$unset'] = query['$unset'] || {};
-  query['$unset'][field] = 1;
+  query['$unset'][field] = '';
 };
 
 /**
@@ -95,4 +95,4 @@ function join (key, prefix) {
   return prefix
     ? prefix + '.' + key
     : key;
-}
+}

package-lock.json

@@ -10,7 +10,7 @@ describe('query()', function () {
 
   it('should $unset null-ish keys', function () {
     var query = diff({ a: 1 }, { a: null });
-    assert(query.$unset.a == 1);
+    assert(query.$unset.a == '');
     assert(!('$set' in query));
   });
 
@@ -23,7 +23,7 @@ describe('query()', function () {
   it('should work with nested keys', function () {
     var query = diff({ a: { b: 1, c: 2 }}, { a: { b: 2, c: null }});
     assert(query.$set['a.b'] == 2);
-    assert(query.$unset['a.c'] == 1);
+    assert(query.$unset['a.c'] == '');
   });
 
   describe('when given a filter', function () {