Incorrect JUnit XML for error outside of test case

[gbruer15]

I encountered an issue trying to convert JUnit XML output from TestReports.jl to html using any package. None of them were displayed the result from an exception being thrown.

I couldn't find a clear definition for what the XML format is supposed to be, but I believe the element needs to be wrapped in a element for other packages to parse it correctly.

Below, I have example tests that throw errors and my proposed fix.

using Test
using TestReports

# Current behavior
ts = @testset ReportingTestSet "" begin
    @testset "Normal tests" begin
        @test true
        @test false
    end
    @testset "Error inside test" begin
        @test true
        @test false
        @test doesntexist == 1
    end
    @testset "Error outside test" begin
        @test true
        @test false
        a = doesntexist
    end
end
println("This XML puts <error> as direct children of <testsuite>")
TestReports.EzXML.prettyprint(report(ts))


# Update to put error result inside a test case.
function TestReports.to_xml(v::TestReports.Error)
    message, type, ntest = TestReports.get_error_info(v)
    x_error = TestReports.error_xml(message, type, v.backtrace)
    x_testcase = TestReports.testcase_xml(v, [x_error])
    x_testcase, ntest, 0, 1  # Increment number of errors by 1
end

ts = @testset ReportingTestSet "" begin
    @testset "Normal tests" begin
        @test true
        @test false
    end
    @testset "Error inside test" begin
        @test true
        @test false
        @test doesntexist == 1
    end
    @testset "Error outside test" begin
        @test true
        @test false
        a = doesntexist
    end
end
println("This XML puts <error> as direct children of <testcase>")
TestReports.EzXML.prettyprint(report(ts))

[oxinabox]

Seems reasonable. Open a PR?