Bug in ParticleSystem object constructor

[kyzyx]

In physics/system.js, the object initializer (i.e. ParticleSystem({repulsion:1000, stiffness:80)) does not work. Changing lines 20-21 from

if (typeof stiffness=='object'){
    var _p = stiffness

to

if (typeof repulsion=='object'){
    var _p = repulsion

fixes the problem