[tiler] sizerThickness default should be 0.0

Change-Id: I9aacd7db8535aee72f0eec1e828c2517d6552bf0
diff --git a/lib/tiler/lib/src/tile.dart b/lib/tiler/lib/src/tile.dart
index ac5dd3b..6b13393 100644
--- a/lib/tiler/lib/src/tile.dart
+++ b/lib/tiler/lib/src/tile.dart
@@ -24,7 +24,7 @@
     @required this.model,
     @required this.chromeBuilder,
     this.sizerBuilder,
-    this.sizerThickness,
+    this.sizerThickness = 0.0,
   });
 
   @override
diff --git a/lib/tiler/lib/src/tiler.dart b/lib/tiler/lib/src/tiler.dart
index 22b36f5..4d7125b 100644
--- a/lib/tiler/lib/src/tiler.dart
+++ b/lib/tiler/lib/src/tiler.dart
@@ -22,7 +22,7 @@
     @required this.model,
     @required this.chromeBuilder,
     this.sizerBuilder,
-    this.sizerThickness,
+    this.sizerThickness = 0.0,
   });
 
   @override