Return node when it contains the other node - with unit test

Fix Colingo#1

index.js

@@ -10,8 +10,10 @@ function getCommonAncestor(node) {
     }
 
     var nodes = slice.call(arguments, 1)
+    var list = parents(node)
+    list.unshift(node)
 
-    return parents(node).filter(function (parent) {
+    return list.filter(function (parent) {
         return nodes.every(function (node) {
             return contains(parent, node)
         })

test/index.js

@@ -17,6 +17,20 @@ test("is correct", function (assert) {
     assert.end()
 })
 
+test("is correct with inner child", function (assert) {
+    var one = elem()
+    var two = elem()
+    var three = elem()
+
+    one.appendChild(two)
+    two.appendChild(three)
+
+    var ancestor = commonAncestors(two, three)
+
+    assert.equal(ancestor, two)
+    assert.end()
+})
+
 test("doesn't return false positives", function (assert) {
     var one = elem()
     var two = elem()