Update libpng to v1.6.34 for cmake
authorYong Tang <yong.tang.github@outlook.com>
Sat, 14 Apr 2018 19:00:36 +0000 (19:00 +0000)
committerYong Tang <yong.tang.github@outlook.com>
Mon, 16 Apr 2018 19:39:00 +0000 (19:39 +0000)
commit21ba571a5ca4072de772cd81a759a3d7a869fd8a
treee93ee586453bf3883af2bfa38162b8f1a70e3f5e
parentf7da45918a6e0d7981eeb2ddf03439ace17f3af7
Update libpng to v1.6.34 for cmake

The libpng has been updated from v1.2.53 to v1.6.34 in PR 18299.
However, the cmake version of libpng has not been updated yet.
This fix updates the libpng for cmake to v1.6.34.

The fix is tested with cmake on linux:
```
tensorflow/tools/ci_build/ci_build.sh CMAKE tensorflow/tools/ci_build/builds/cmake.sh
```

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
tensorflow/contrib/cmake/external/png.cmake