tests: add reference files for julia@1.3.1

Some tests only run for older Julia versions,
these reference files are thus only generated
for the first time when run with an older julia
version.

Author: ReubenJ

test/reference_outputs/typed_method_signatures_k6_pre_16.txt

@@ -0,0 +1,6 @@
+
+```julia
+k_6(x::Array{T<:Number,1}) -> Array{T,1} where T<:Number
+
+```
+

test/reference_outputs/typed_method_signatures_not_windows_or_not_pre_18.txt

@@ -0,0 +1,8 @@
+
+```julia
+h_1(
+x::Union{Array{T,3},Array{T,4}}whereT
+)->Union{Array{T,3},Array{T,4}}whereT
+
+```
+

test/reference_outputs/typed_method_signatures_windows_18_and_later.txt

@@ -206,10 +206,11 @@ ro_path(fn) = joinpath(@__DIR__, "reference_outputs", fn)
                 :module => M,
             )
             str = @io2str DSE.format(DSE.TYPEDSIGNATURES, ::IO, doc)
+            str = replace(str, " " => "") 
             if Sys.iswindows() && VERSION < v"1.8"
                 @test_reference ro_path("typed_method_signatures_windows_pre_18.txt") str
             else
-                @test_reference ro_path("typed_method_signatures_windows_18_and_later.txt") str
+                @test_reference ro_path("typed_method_signatures_not_windows_or_not_pre_18.txt") str
             end
 
             doc.data = Dict(