Fix typo in shader test
Fix typo in shader test

The only error in the test should be the non-integer index. gl_FragColor
should be used correctly.

BUG=angleproject:1254
TEST=angle_unittests

Change-Id: I0b7a36be5485661cc03bf2c476aaacae5d3b6e76
Reviewed-on: https://chromium-review.googlesource.com/320280
Tested-by: Olli Etuaho <38ae6c0e2772a20e8e989f80cb8c99d274e44242@nvidia.com>
Reviewed-by: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ecoal95/angle,ppy/angle,mlfarrell/angle,MSOpenTech/angle,domokit/waterfall,mikolalysenko/angle,ecoal95/angle,ppy/angle,mlfarrell/angle,mikolalysenko/angle,MSOpenTech/angle,ecoal95/angle,MSOpenTech/angle,ecoal95/angle,mlfarrell/angle,ppy/angle,mikolalysenko/angle,MSOpenTech/angle,domokit/waterfall,ppy/angle,mikolalysenko/angle,ecoal95/angle,mlfarrell/angle