devserver: fix KeyError messages.

BUG=None
TEST=None

Change-Id: I2b632cdfbb695a44c34d7c4e4bdfd2080c5ca4e7
Reviewed-on: https://chromium-review.googlesource.com/767114
Commit-Ready: Xixuan Wu <xixuan@chromium.org>
Tested-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/devserver.py b/devserver.py
index 58eba3b..af7df5b 100755
--- a/devserver.py
+++ b/devserver.py
@@ -156,7 +156,7 @@
 # Auto-update parameters
 
 # Error msg for missing key in CrOS auto-update.
-KEY_ERROR_MSG = 'Key Error in cmd %s: %s= is required'
+KEY_ERROR_MSG = 'Key Error in RPC: %s= is required'
 
 # Command of running auto-update.
 AUTO_UPDATE_CMD = '/usr/bin/python -u %s -d %s -b %s --static_dir %s'