Add netcdftime as a dependency

[lbdreyer]

As netcdf4 v1.4.0, netcdftime has been removed and so needs to be added as a separate dependency

The conda-forge recipe will also need updating

The conda build of cf_units v1.2 will also need updating (The latestcf_units has removed the dependency on netcdftime)

[lbdreyer]

Example failure: https://travis-ci.org/SciTools/iris/jobs/376920636

[bjlittle]

👍 Thanks @lbdreyer, but we're going to resolve this with #3016

[lbdreyer]

I've updated the iris 2.0.0 recipe so that people who are getting iris from conda-forge, pick up a version of netcdf4 that works:
conda-forge/iris-feedstock#28

I've had a couple of people asking about this.

[pp-mo]

@bjlittle we're going to resolve this with #3016

I think this is now taking too long, and we have a backlog of PRs that aren't getting merged.
@pelson @bjlittle can we reconsider this PR, just to unblock Travis testing on Iris ?

[pp-mo]

can we reconsider this PR

It seems to need a rebase. I might try that myself ...
How about : #3017 replaces ???

[pelson]

How about : #3017 replaces ???

OK.

[pelson]

I think this is now taking too long

I agree. Let's get our tests passing before we try moving forwards.