Correct credits for the calculator plugin


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@10804 a1c6a512-1295-4272-9138-f99709370657
diff --git a/docs/CREDITS b/docs/CREDITS
index ca2801c..e4c9e92 100644
--- a/docs/CREDITS
+++ b/docs/CREDITS
@@ -234,4 +234,5 @@
 Vadim Chekan
 Christopher Borcsok
 Victor Cardenas
-Andrew Melville
\ No newline at end of file
+Andrew Melville
+Pengxuan Liu