Update Camera.js

Set default Camera.roundPx value to false, in order to prevent almost-1-px jitter  (Pixi does subpixel rendering on (almost?) everything else in Phaser, so rounding here is not okay). 

@ next cleanup: remove this bool completely if there's no problems with the new default value.

This should solve issue #1377  and is how issue #1141 was supposed to be solved

Only caveat: this may have undesired side effects in some situations, as I dont know why this rounding was added in the first place..