updating doc

Author: josslynzhang

docs/resources/marker_setting.md

@@ -26,7 +26,7 @@ The following arguments are supported:
 
 * `dataset` - (Required) The dataset this marker setting is placed on.
 * `type` - (Required) The type of the marker setting, Honeycomb.io can display markers in different colors depending on their type.
-* `color` - (Optional) The color set for the marker as a hex color code (e.g. `#DF4661`)
+* `color` - (Required) The color set for the marker as a hex color code (e.g. `#DF4661`)
 
 ## Attribute Reference