example: cleanup readme and pubspec (#1270)

Author: kevmoo

example/README.md

@@ -5,11 +5,11 @@ dependencies to your `pubspec.yaml`.
 
 ```yaml
 dependencies:
-  json_annotation: ^4.7.0
+  json_annotation: ^4.8.0
 
 dev_dependencies:
-  build_runner: ^2.0.0
-  json_serializable: ^6.0.0
+  build_runner: ^2.3.3
+  json_serializable: ^6.6.0
 ```
 
 Annotate your code with classes defined in
@@ -23,7 +23,7 @@ Annotate your code with classes defined in
 Run `dart run build_runner build` to generate files into your source directory.
 
 ```console
-> pub run build_runner build
+> dart pub run build_runner build
 [INFO] ensureBuildScript: Generating build script completed, took 368ms
 [INFO] BuildDefinition: Reading cached asset graph completed, took 54ms
 [INFO] BuildDefinition: Checking for updates since last build completed, took 663ms

example/pubspec.yaml

@@ -5,24 +5,29 @@ environment:
   sdk: '>=2.18.0 <3.0.0'
 
 dependencies:
-  json_annotation: ^4.7.0
+  json_annotation: ^4.8.0
 
 dev_dependencies:
   # Used by tests. Not required to use `json_serializable`.
   _json_serial_shared_test:
     path: ../shared_test
-  build_runner: ^2.0.0
+
+  # REQUIRED!
+  build_runner: ^2.3.3
 
   # Used by tests. Not required to use `json_serializable`.
   build_verify: ^3.0.0
 
-  json_serializable: ^6.0.0
+  # REQUIRED!
+  json_serializable: ^6.6.0
 
   # Not required to use `json_serializable`.
   lints: ^2.0.0
   path: ^1.8.0
   test: ^1.16.0
 
+# This section is used to verify changes to these packages. Do not include in
+# your code!
 dependency_overrides:
   json_annotation:
     path: ../json_annotation

example/test/readme_test.dart

@@ -25,9 +25,9 @@ void _expect(String fileName) {
 
 const _pubspecContent = r'''
 dependencies:
-  json_annotation: ^4.7.0
+  json_annotation: ^4.8.0
 
 dev_dependencies:
-  build_runner: ^2.0.0
-  json_serializable: ^6.0.0
+  build_runner: ^2.3.3
+  json_serializable: ^6.6.0
 ''';