Fix a doc typo.

R=rsc
APPROVED=rsc
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=30967
CL=30990

doc/effective_go.html

@@ -360,7 +360,7 @@ out a data structure.
 <h3 id="buffer-slice">Use parallel assignment to slice a buffer</h3>
 
 <pre>
-hdr, body, checksum := buf[0:20], buf[20:len(buf)], buf[len(buf)-4:len(buf)];
+hdr, body, checksum := buf[0:20], buf[20:len(buf)-4], buf[len(buf)-4:len(buf)];
 </pre>
 
 <h2 id="control-flow">Control Flow</h2>