Fix documentation bugs 7517 and 7518 in serialization.

pkg/serialization/lib/src/reader_writer.dart

Index: pkg/serialization/lib/src/reader_writer.dart
diff --git a/pkg/serialization/lib/src/reader_writer.dart b/pkg/serialization/lib/src/reader_writer.dart
index 586e115a15431d971ab3483fe69b94bc16b1abc3..ffda2096257d6ae7f9f818a7135c88c31ab6a7cd 100644
--- a/pkg/serialization/lib/src/reader_writer.dart
+++ b/pkg/serialization/lib/src/reader_writer.dart
@@ -55,7 +55,7 @@ class Writer {
 
   /**
    * Creates a new [Writer] that uses the rules from its parent
-   * [Serialization]. Serializations are do not keep any state
+   * [Serialization]. Serializations do not keep any state
    * related to a particular read/write, so the same one can be used
    * for multiple different Readers/Writers.
    */