update lpinyin to null safety version

example/pubspec.lock

@@ -198,12 +198,10 @@ packages:
   lpinyin:
     dependency: transitive
     description:
-      path: "."
-      ref: HEAD
-      resolved-ref: d39049042658dffcf9f6bd936cd52c1919a90b1a
-      url: "https://github.com/flutterchina/lpinyin"
-    source: git
-    version: "2.0.0"
+      name: lpinyin
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "2.0.1"
   meta:
     dependency: transitive
     description:

pubspec.lock

@@ -156,12 +156,10 @@ packages:
   lpinyin:
     dependency: "direct main"
     description:
-      path: "."
-      ref: HEAD
-      resolved-ref: d39049042658dffcf9f6bd936cd52c1919a90b1a
-      url: "https://github.com/flutterchina/lpinyin"
-    source: git
-    version: "2.0.0"
+      name: lpinyin
+      url: "https://pub.flutter-io.cn"
+    source: hosted
+    version: "2.0.1"
   matcher:
     dependency: transitive
     description:

pubspec.yaml

@@ -12,8 +12,7 @@ dependencies:
     sdk: flutter
   flutter_screenutil: ^5.0.0-nullsafety.7
   flutter_easyrefresh: ^2.1.8
-  lpinyin: 
-    git: https://github.com/flutterchina/lpinyin
+  lpinyin: ^2.0.1
   image_picker: ^0.7.2
   bot_toast: ^4.0.0+1
   velocity_x: