opt out of mono on travis

[SimonCropp]

looks like mono is not being used? if it is then close this

But if it isnt this PR will speed up your travis builds

[JimBobSquarePants]

I've restarted the Travis build here. The first run had some Gdip errors, so I'm hoping it was a one-time issue.

[JimBobSquarePants]

@SimonCropp Looks like this won't work as it is.

System.DllNotFoundException : Unable to load DLL 'libgdiplus': The specified module could not be found.

https://travis-ci.org/SixLabors/ImageSharp/builds/602052654#L484

Updating to the latest System.Drawing.Common should hopefully fix it.
dotnet/core#2746

[JimBobSquarePants]

See comments regarding missing libgdiplus

[codecov]

Codecov Report

Merging #1032 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1032      +/-   ##
==========================================
+ Coverage   89.87%   89.87%   +<.01%     
==========================================
  Files        1103     1103              
  Lines       48896    48897       +1     
  Branches     3441     3441              
==========================================
+ Hits        43944    43945       +1     
  Misses       4249     4249              
  Partials      703      703

Impacted Files	Coverage Δ
.../PixelFormats/PixelBlenders/PorterDuffFunctions.cs	100% <0%> (ø)	⬆️
...rc/ImageSharp/PixelFormats/PixelBlender{TPixel}.cs	100% <0%> (ø)	⬆️
...ats/PixelBlenders/PorterDuffFunctions.Generated.cs	38.02% <0%> (ø)	⬆️
...ts/PixelBlenders/DefaultPixelBlenders.Generated.cs	77.77% <0%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2925668...a1a6032. Read the comment docs.

[SimonCropp]

i pushed System.Drawing.Common 4.6 to check

[JimBobSquarePants]

Same issue I'm afraid. I've cancelled the AppVeyor build to stop it blocking others.

[SimonCropp]

trying this dotnet/core#2746 (comment)

[JimBobSquarePants]

Fixed with #1082