Fixes Future<void> issue in Shrine. (#28)

jsonexample/ios/Runner.xcworkspace/xcshareddata/WorkspaceSettings.xcsettings

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>BuildSystemType</key>
+	<string>Original</string>
+</dict>
+</plist>

jsonexample/pubspec.yaml

@@ -7,19 +7,22 @@ environment:
 dependencies:
   json_annotation: ^1.0.0
   built_collection: '>=2.0.0 <5.0.0'
-  built_value: ^6.1.0
+  built_value: ^6.1.5
 
   flutter:
     sdk: flutter
 
 dev_dependencies:
-  build_runner: '>=0.9.0 <0.11.0'
+  build_runner: ^1.0.0
-  built_value_generator: ^6.1.0
+  built_value_generator: ^6.1.5
   json_serializable: ^1.0.0
 
   flutter_test:
     sdk: flutter
 
+dependency_overrides:
+  analyzer: 0.33.0
+
 flutter:
 
   uses-material-design: true

shrine/ios/Runner.xcworkspace/xcshareddata/WorkspaceSettings.xcsettings

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>BuildSystemType</key>
+	<string>Original</string>
+</dict>
+</plist>

shrine/lib/expanding_bottom_sheet.dart

@@ -381,7 +381,8 @@ class _ExpandingBottomSheetState extends State<ExpandingBottomSheet> with Ticker
   // only be relevant for Android).
   Future<bool> _onWillPop() async {
     if (!_isOpen) {
-      return SystemNavigator.pop();
+      await SystemNavigator.pop();
+      return true;
     }
 
     close();