fix saving as .tikz (#2901)

src/output.jl

@@ -112,7 +112,7 @@ function savefig(plt::Plot, fn::AbstractString)
     fn = abspath(expanduser(fn))
 
     # get the extension
-    fn, ext = splitext(fn)
+    _, ext = splitext(fn)
     ext = chop(ext, head = 1, tail = 0)
     if isempty(ext)
         ext = defaultOutputFormat(plt)

test/test_pgfplotsx.jl

@@ -302,6 +302,11 @@ end
             lines = readlines(io)
             @test count(s -> occursin("node", s), lines) == 9
          end
+         # test .tikz extension
+         file_path =joinpath(path,"annotations.tikz")
+         @test_nowarn savefig(annotation_plot, file_path)
+         @test_nowarn open(file_path) do io
+         end
       end
    end # testset
    @testset "Ribbon" begin