Update coverage usage example (#1757)

- Use `dart pub` instead of `pub`
- Point `--packages` to `.dart_tool/package_config.json` as suggested by the `coverage` package.

Co-authored-by: Nate Bosch <nbosch@google.com>
diff --git a/pkgs/test/CHANGELOG.md b/pkgs/test/CHANGELOG.md
index 8641c0d..241f960 100644
--- a/pkgs/test/CHANGELOG.md
+++ b/pkgs/test/CHANGELOG.md
@@ -1,6 +1,7 @@
 ## 1.21.6-dev
 
 * Require Dart >= 2.18.0
+* Fix the coverage usage example in the README.md
 
 ## 1.21.5
 
diff --git a/pkgs/test/README.md b/pkgs/test/README.md
index 8f4fe09..e6f7dd7 100644
--- a/pkgs/test/README.md
+++ b/pkgs/test/README.md
@@ -278,7 +278,7 @@
 dart pub global activate coverage
 
 ## Format collected coverage to LCOV (only for directory "lib")
-pub global run coverage:format_coverage --packages=.packages --report-on=lib --lcov -o ./coverage/lcov.info -i ./coverage
+dart pub global run coverage:format_coverage --packages=.dart_tool/package_config.json --report-on=lib --lcov -o ./coverage/lcov.info -i ./coverage
 
 ## Generate LCOV report:
 genhtml -o ./coverage/report ./coverage/lcov.info