Fix Tuple2 type

lib/flutter_quill.dart

@@ -1,7 +1 @@
-library flutter_quill;
-
-/// A Calculator.
-class Calculator {
-  /// Returns [value] plus 1.
-  int addOne(int value) => value + 1;
-}
+library flutter_quill;

lib/widgets/default_styles.dart

@@ -76,7 +76,7 @@ class DefaultStyles {
       fontSize: 16.0,
       height: 1.3,
     );
-    Tuple2 baseSpacing = Tuple2(6.0, 10);
+    Tuple2<double, double> baseSpacing = Tuple2(6.0, 10);
     String fontFamily;
     switch (themeData.platform) {
       case TargetPlatform.iOS:

test/flutter_quill_test.dart

@@ -1,13 +0,0 @@
-import 'package:flutter_test/flutter_test.dart';
-
-import 'package:flutter_quill/flutter_quill.dart';
-
-void main() {
-  test('adds one to input values', () {
-    final calculator = Calculator();
-    expect(calculator.addOne(2), 3);
-    expect(calculator.addOne(-7), -6);
-    expect(calculator.addOne(0), 1);
-    expect(() => calculator.addOne(null), throwsNoSuchMethodError);
-  });
-}