doc: replace pub run with dart run

.github/workflows/test-package.yml

diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index b6c20a5..838a553 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -47,7 +47,7 @@
         name: Install dependencies
         run: dart pub get
       - name: Build generated artifacts
-        run: dart pub run build_runner build
+        run: dart run build_runner build
       - name: Analyze code
         run: dart analyze --fatal-infos
 

NULL_SAFETY_README.md

diff --git a/NULL_SAFETY_README.md b/NULL_SAFETY_README.md
index ebf2434..c9045db 100644
--- a/NULL_SAFETY_README.md
+++ b/NULL_SAFETY_README.md
@@ -101,7 +101,7 @@
 The final step is to run build_runner in order to generate the new library:
 
 ```shell
-flutter pub run build_runner build
+dart run build_runner build
 # OR
 dart run build_runner build
 ```

README.md

diff --git a/README.md b/README.md
index a9fdfac..3b94a5d 100644
--- a/README.md
+++ b/README.md
@@ -49,7 +49,7 @@
 The next step is to run `build_runner` in order to generate this new library:
 
 ```shell
-flutter pub run build_runner build
+dart run build_runner build
 # OR
 dart run build_runner build
 ```

test/all.dart

diff --git a/test/all.dart b/test/all.dart
index 5fcc7b4..c2c11b0 100644
--- a/test/all.dart
+++ b/test/all.dart
@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // This file explicitly does _not_ end in `_test.dart`, so that it is not picked
-// up by `pub run test`. It is here for coveralls.
+// up by `dart run test`. It is here for coveralls.
 
 import 'builder/auto_mocks_test.dart' as builder_auto_mocks_test;
 import 'builder/custom_mocks_test.dart' as builder_custom_mocks_test;