Downgrade to mocha@2.3.4

[tschaub]

See #4726 (comment).

Also related:

• Travis --no-color, truncated test cases mochajs/mocha#2060
• Travis --no-color, truncated test cases mochajs/mocha#2060

And more upgrade hazards:

• Breaking change from version 2.4.2 to 2.4.3 mochajs/mocha#2080 (see also the hanging tests on displayName for attributes #243)

Before upgrading mocha, let's confirm npm test works locally and that the output is readable on Travis.

[tschaub]

Before:

After:

[marcjansen]

This looks good to me, thanks and please merge!

[boneskull]

@tschaub @marcjansen et al

Please see this build with the proposed fix, and the summary of changes.

If everything looks good, I will merge and release this so you guys can get back on track with new versions.

[marcjansen]

Thanks for pinging us, @boneskull. We'll definitely check this.

[tschaub]

Thanks @boneskull. Here's a build in progress: https://travis-ci.org/openlayers/ol3/builds/105522588

All looks good locally. Thanks for the work on this, and for reaching out about the fix.