fix grammer in .gitignore error message (#2995)
diff --git a/lib/src/validator/gitignore.dart b/lib/src/validator/gitignore.dart
index 047647d..df01214 100644
--- a/lib/src/validator/gitignore.dart
+++ b/lib/src/validator/gitignore.dart
@@ -60,7 +60,7 @@
if (ignoredFilesCheckedIn.isNotEmpty) {
warnings.add('''
-${ignoredFilesCheckedIn.length} checked in ${pluralize('file', ignoredFilesCheckedIn.length)} are ignored by a `.gitignore`.
+${ignoredFilesCheckedIn.length} checked in ${pluralize('file', ignoredFilesCheckedIn.length)} ${ignoredFilesCheckedIn.length == 1 ? 'is' : 'are'} ignored by a `.gitignore`.
Previous versions of Pub would include those in the published package.
Consider adjusting your `.gitignore` files to not ignore those files, and if you do not wish to
