Remove workaround for dart-lang/language#1785

PiperOrigin-RevId: 415353392

Author: stereotype441

charts_flutter/lib/src/chart_canvas.dart

@@ -150,9 +150,7 @@ class ChartCanvas implements common.ChartCanvas {
       common.Color? stroke,
       double? strokeWidthPx,
       Rectangle<num>? drawAreaBounds}) {
-    // TODO: remove this explicit `bool` type when no longer needed
-    // to work around https://github.com/dart-lang/language/issues/1785
-    final bool drawStroke =
+    final drawStroke =
         (strokeWidthPx != null && strokeWidthPx > 0.0 && stroke != null);
 
     final strokeWidthOffset = (drawStroke ? strokeWidthPx : 0);

charts_flutter/pubspec.yaml

@@ -4,7 +4,7 @@ description: Material Design charting library for flutter.
 homepage: https://github.com/google/charts
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '>=2.15.0 <3.0.0'
   flutter: '>=2.5.0'
 
 dependencies: