make layer type change go through a source refresh,

- staying safe as some type change lead to exceptions

Author: etpinard

src/plots/mapbox/layers.js

@@ -48,16 +48,13 @@ proto.update = function update(opts) {
 proto.needsNewSource = function(opts) {
 
     // for some reason changing layer to 'fill' or 'symbol'
-    // w/o changing the source throws an exception in mapbox-gl 0.18
-
-    var changesToFill = (this.layerType !== 'fill' && opts.type === 'fill'),
-        changesToSymbol = (this.layerType !== 'symbol' && opts.type === 'symbol');
+    // w/o changing the source throws an exception in mapbox-gl 0.18 ;
+    // stay safe and make new source on type changes
 
     return (
         this.sourceType !== opts.sourcetype ||
         this.source !== opts.source ||
-        changesToFill ||
-        changesToSymbol
+        this.layerType !== opts.type
     );
 };