Drop Julia 0.6

[rdeits]

Fixes #67

[codecov-io]

Codecov Report

Merging #69 into master will not change coverage.
The diff coverage is 0%.

@@         Coverage Diff          @@
##           master   #69   +/-   ##
====================================
  Coverage       0%    0%           
====================================
  Files          12    12           
  Lines         304   302    -2     
====================================
+ Misses        304   302    -2

Impacted Files	Coverage Δ
src/geometry.jl	0% <ø> (ø)	⬆️
src/MeshCat.jl	0% <ø> (ø)	⬆️
src/servers.jl	0% <0%> (ø)	⬆️
src/msgpack.jl	0% <0%> (ø)	⬆️
src/trees.jl	0% <0%> (ø)	⬆️
src/animations.jl	0% <0%> (ø)	⬆️

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