enableEditCell update to allow colDef.enableCellEdit to override config.enableCellEdit

I noticed a bug in v2.0.4 where colDef.enableCellEdit will not override the config.enableCellEdit (e.g. if config is set to false and colDef is set to true then with the current OR test the value will be set to false, even though it is expected that colDef should override config). On line 675 of ng-grid-2.0.4.debug.js I updated the code from:
    self.enableCellEdit = config.enableCellEdit || colDef.enableCellEdit;
to become:
    self.enableCellEdit = colDef.hasOwnProperty('enableCellEdit') ? colDef.enableCellEdit : config.enableCellEdit;

So now if the colDef has been set this value is used for the column, otherwise the config value is taken.