Update name for Olaf in perface

I guess we don't mapping github account to the name correctly during making
preface.adoc :P

Author: kito-cheng

doc/preface.adoc

@@ -17,14 +17,14 @@ This RISC-V specification has been contributed to directly or indirectly by (in
 Contributors to all versions of the spec in alphabetical order:
 
 Brandon Wu,
-Camel Coder,
 Craig Topper,
 Eop Chen,
 HanKuan Chen,
 HsiangKai Wang,
 Jerry Zhang Jian,
 Kito Cheng,
 Nick Knight,
+Olaf Bernstein,
 Roger Ferrer Ibanez,
 Yi-Hsiu Hsu,
 Zakk Chen