Update charts_flutter to 0.12.0 (#951)

web/charts/pubspec.lock

@@ -14,16 +14,14 @@ packages:
       name: charts_common
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.11.0"
+    version: "0.12.0"
   charts_flutter:
     dependency: "direct main"
     description:
-      path: charts_flutter
-      ref: HEAD
-      resolved-ref: "30477090290b348ed3101bc13017aae465f59017"
-      url: "https://github.com/google/charts"
-    source: git
-    version: "0.11.0"
+      name: charts_flutter
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.12.0"
   clock:
     dependency: transitive
     description:
@@ -106,3 +104,4 @@ packages:
     version: "2.1.0"
 sdks:
   dart: ">=2.12.0 <3.0.0"
+  flutter: ">=2.5.0"

web/charts/pubspec.yaml

@@ -8,10 +8,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  charts_flutter: 
-    git:
-      url: https://github.com/google/charts
-      path: charts_flutter
+  charts_flutter: ^0.12.0
   meta: ^1.1.1
   intl: ^0.17.0