Update path where the local version of cmake lives.
Update path where the local version of cmake lives.

This should fix the Travis CI build in PR #118.

mmp/pbrt-v3,nyue/pbrt-v3,mmp/pbrt-v3,nispaur/pbrt-v3,nyue/pbrt-v3,mmp/pbrt-v3,shihchinw/pbrt-v3,shihchinw/pbrt-v3,nispaur/pbrt-v3,nyue/pbrt-v3,nyue/pbrt-v3,nispaur/pbrt-v3,shihchinw/pbrt-v3,nispaur/pbrt-v3,mmp/pbrt-v3,shihchinw/pbrt-v3