rebaseline_server: fix sorting by perceptual diff column

(SkipBuildbotRuns)
BUG=skia:2410
NOTREECHECKS=True
NOTRY=True
R=rmistry@google.com
TBR=rmistry

Author: epoger@google.com

Review URL: https://codereview.chromium.org/235993002

git-svn-id: http://skia.googlecode.com/svn/trunk@14167 2bbb7eff-a529-9590-31e7-b0007b416f81
2 files changed