fix tests on julia 0.7

[bjarthur]

• [x ] I've run the regression tests
• [x ] I've squash'ed or fixup'ed junk commits with git-rebase

test/testscripts/colored_boxplot.jl was failing on julia 0.7. this fixes that.

worth nothing that there appears to be a breaking change with julia 1.1 regarding broadcasting:

$ julia7
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: https://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.7.0 (2018-08-08 06:46 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-apple-darwin14.5.0

julia> first.(keys(Dict('a'=>1,'b'=>2)))
┌ Warning: broadcast will default to iterating over its arguments in the future. Wrap arguments of
│ type `x::Base.KeySet{Char,Dict{Char,Int64}}` with `Ref(x)` to ensure they broadcast as "scalar" elements.
│   caller = ip:0x0
└ @ Core :-1
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

julia> 

$ julia1
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.1.0 (2019-01-21)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org/ release
|__/                   |

julia> first.(keys(Dict('a'=>1,'b'=>2)))
2-element Array{Char,1}:
 'a'
 'b'

[codecov-io]

Codecov Report

Merging #1260 into master will increase coverage by 4.99%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1260      +/-   ##
==========================================
+ Coverage   85.34%   90.33%   +4.99%     
==========================================
  Files          36       36              
  Lines        4148     3943     -205     
==========================================
+ Hits         3540     3562      +22     
+ Misses        608      381     -227

Impacted Files	Coverage Δ
src/statistics.jl	96.84% <100%> (+6.22%)	⬆️
src/geom/bar.jl	93.23% <0%> (+1.38%)	⬆️
src/shapes.jl	100% <0%> (+1.96%)	⬆️
src/geom/polygon.jl	94.87% <0%> (+2.37%)	⬆️
src/mapping.jl	85.43% <0%> (+2.41%)	⬆️
src/geom/segment.jl	94.44% <0%> (+2.55%)	⬆️
src/guide.jl	87.87% <0%> (+3.48%)	⬆️
src/guide/keys.jl	94.73% <0%> (+3.59%)	⬆️
src/coord.jl	88.17% <0%> (+3.63%)	⬆️
src/color_misc.jl	62.06% <0%> (+4%)	⬆️
... and 14 more

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