CI Update

[CiaranOMara]

This pull request was created in response to #1339 (comment).

Proposed changes

• Add Julia 1.3 to test matrix.
• Use the codecov flag in Travis instead of the manual code version.
• Pkg.instantiate after Pkg.develop.
• Add colour to make doc output.
• Move tests with Compose.jl#master into an Edge stage.

Moving tests using Compose.jl#master into their own stage provides visibility for new development while prioritising Gadfly.jl#master.

[codecov-io]

Codecov Report

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@@            Coverage Diff            @@
##             master    #1340   +/-   ##
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  Coverage          ?   90.12%           
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  Files             ?       36           
  Lines             ?     3940           
  Branches          ?        0           
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  Hits              ?     3551           
  Misses            ?      389           
  Partials          ?        0

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[CiaranOMara]

I wasn't sure how to best structure this pull request. Anyhow, I've added Cairo.jl compatibility changes on the back of this PR as it not only shows improvement across operating systems, it also shows how the Edge stage works - you'll notice that many of the deprecation warnings are already addressed by Compose.jl#master.

[Mattriks]

I assume this PR will close #1320 and #1324. If so, add that to your first post above (https://help.github.com/en/github/managing-your-work-on-github/closing-issues-using-keywords)

[bjarthur]

it'd be better to have the Cairo dependency commit in a separate PR. i'd merge that right away.

regarding 1.3, again, i'd suggest holding off on that until it is actually released, and stop testing on 1.2 at the same time.

i also don't understand the Edge job. i'm just being dumb here i think. can you please explain how this is different?

[CiaranOMara]

Previously, by way of the before_script, all tests were performed using Compose.jl#master. With this PR, tests in the Test job use a Compose.jl release and tests in the Edge job use Compose.jl#master. With this configuration, the tests in the Test job test the packages installed by the end-user, and the tests in the Edge job shows developers how Gadfly.jl is performing with the latest Compose.jl developments.

[CiaranOMara]

I have moved the Cairo compatibility change to #1343.

[CiaranOMara]

I have removed Julia v1.3 from the test matrix.

[CiaranOMara]

The Edge stage does not seem quite right as it does not appear to be allowed to fail.