Add missing root for DynamicMeasure OL addin

A new OL addin (DynamicMeasure) is included in recent master revisions of CGXP:
https://github.com/camptocamp/cgxp/blob/master/sandbox/FeatureEditing/ux/widgets/FeatureEditingControler.js#L25
but its path is not available in jsbuild config.