DepIndicators: Neutral DependentsIndicator with zero dependents

The old logic was from [1]:

  var dependentsColor = (item) -> (item.done ? green : red)

But the screenshot in depviz.mocks.011.jpg shows grey dependents
indicators for jbenet#1 and jbenet#7 (neither of which have dependencies).

[1]: jbenet#10

src/DepIndicators.js

@@ -56,7 +56,10 @@ class RelatedIndicator extends Component {
 
 class DependentsIndicator extends Component {
   render() {
-    var color = this.props.done ? Green : Red;
+    var color = Neutral;
+    if (this.props.dependents) {
+      color = this.props.done ? Green : Red;
+    }
     var attributes = {};
     if (this.props.transform) {
       attributes.transform = this.props.transform;