Update closure-util

The closure-util package works on Node 0.8, 0.10, and 0.11 (as of this writing), but it requires an updated version of npm to install on Node 0.8.  For the build to pass on Travis, we update npm before installing other dependencies.  For others who are installing the openlayers package, nothing special is required for Node 0.10 and above.  For users on Node 0.8, the openlayers package will only install with an updated version of npm.  This can be installed with npm itself.

    npm install -g npm # only needed on Node 0.8
Merge pull request #2197 from tschaub/deps

Update closure-util.
Add standard docs text to abstract base classes
Merge pull request #2199 from probins/abstract

Add standard docs text to abstract base classes
Pass a replay group to ol.render.Event
Make ol.FeatureOverlay use replay group
Add missing format option to TileVector docs
Add classdesc to remaining vector classes
Remove static button in docs sidebar if none
Merge pull request #2206 from probins/nostatic

Remove static button in docs sidebar if none
Merge pull request #2203 from probins/classdesc

Add classdesc to remaining vector classes
Merge pull request #2202 from probins/tvformat

Add missing format option to TileVector docs
Don't scale the text stroke width by pixel ratio
Use getInExtent instead of forEachInExtent
Merge pull request #2209 from fredj/modify-rbush

Use getInExtent instead of forEachInExtent
Get rid of unused info div in vector-wfs example
Merge pull request #2210 from bartvde/wfs-example-fix

Get rid of unused info div in vector-wfs example
Make the scale factor of ol.format.Polyline configurable

And export the class
Merge pull request #2101 from fredj/polyline-factor

Make the scale factor of ol.format.Polyline configurable
Add "None" to draw-features example's select

This allows to deactivate drawing entirely in the example.