Add syntax highlight tag to example code block

Author: abhro

src/structarray.jl

@@ -136,7 +136,7 @@ julia> StructArray{Complex{Float64}}(X; dims=2)
 ```
 
 By default, fields will be unwrapped until they match the element type of the array:
-```
+```julia-repl
 julia> StructArray{Tuple{Float64,Complex{Float64}}}(rand(3,2); dims=1)
 2-element StructArray(view(::Array{Float64,2}, 1, :), StructArray(view(::Array{Float64,2}, 2, :), view(::Array{Float64,2}, 3, :))) with eltype Tuple{Float64,Complex{Float64}}:
  (0.004767505234193781, 0.27949621887414566 + 0.9039320635041561im)