Update doc comments to follow style guide.

sdk/lib/_internal/pub/bin/pub.dart

Index: sdk/lib/_internal/pub/bin/pub.dart
diff --git a/sdk/lib/_internal/pub/bin/pub.dart b/sdk/lib/_internal/pub/bin/pub.dart
index a10c09b62513a94192cd5bac1aaf07026f37b7c7..94d5ab08a1b271b047c214b4f5c81ab287f6d50b 100644
--- a/sdk/lib/_internal/pub/bin/pub.dart
+++ b/sdk/lib/_internal/pub/bin/pub.dart
@@ -199,8 +199,10 @@ Future invokeCommand(String cacheDir, ArgResults mainOptions) {
   });
 }
 
-/// Checks that pub is running on a supported platform. If it isn't, it prints
-/// an error message and exits. Completes when the validation is done.
+/// Checks that pub is running on a supported platform.
+///
+/// If it isn't, it prints an error message and exits. Completes when the
+/// validation is done.
 Future validatePlatform() {
   return syncFuture(() {
     if (Platform.operatingSystem != 'windows') return null;