Rename variable

This was misnamed before. An XLogData *has* a message, but it is not
itself a message.

Author: jgaskins

spec/pg/replication_spec.cr

@@ -11,7 +11,7 @@ class TestMessageHandler
     h[k] = {} of Bytes => PG::Replication::WALMessage::TupleData
   }
 
-  def received(msg : PG::Replication::XLogData, connection : PG::Replication::Connection, &)
+  def received(data : PG::Replication::XLogData, connection : PG::Replication::Connection, &)
     yield
     connection.last_wal_byte_flushed = msg.wal_end
     connection.last_wal_byte_applied = msg.wal_end

src/pg/replication.cr

@@ -24,7 +24,7 @@ module PG::Replication
     #   end
     # end
     # ```
-    abstract def received(msg : PG::Replication::XLogData, connection : PG::Replication::Connection, &)
+    abstract def received(data : PG::Replication::XLogData, connection : PG::Replication::Connection, &)
 
     def received(frame)
     end