Fixes for removal of deprecations in ImageCore

[timholy]

Note the temporary hack to .travis.yml just so this can be tested on some machine besides mine.

[timholy]

Looks fine. I'll back out the .travis.yml change and then merge. Tests won't pass, but now we know they do with the right dependencies.

[codecov]

Codecov Report

Merging #24 into master will decrease coverage by 1.51%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
- Coverage     100%   98.48%   -1.52%     
==========================================
  Files           1        1              
  Lines         129      132       +3     
==========================================
+ Hits          129      130       +1     
- Misses          0        2       +2

Impacted Files	Coverage Δ
src/ImageAxes.jl	98.48% <60%> (-1.52%)	⬇️

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[timholy]

(Record of successful test on 0.6: https://travis-ci.org/JuliaImages/ImageAxes.jl/builds/293244119?utm_source=github_status&utm_medium=notification)