lerpColor: round float to int instead of truncate.

It is done to match latest processing change: https://github.com/processing/processing/pull/2813
The lerp.pde test is updated with values computed with latest processing.
Yea, `| 0` rulez!!! `<< 0`, `>> 0`, `~~` also work!  :P
Take a look at this thread too: https://github.com/lmccart/p5.js/issues/469