tests failing for uppercase words

[tj]

we have cases where the user-input is all caps, so "FOOBAR" becomes "f_o_o_b_a_r", went to go patch but the tests are failing as well:

--- FAIL: TestUnderscoreAcronymSequence (0.00 seconds)
    inflect_test.go:12: inflect: expected html5_html_api got h_t_m_l5_h_t_m_l_a_p_i 
         /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:12 (0x3d546)
            com/segmentio/inflect.assertEqual: t.Errorf("inflect: expected %v got %v \n %s", a, b, debug.Stack())
        /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:440 (0x3e55b)
            com/segmentio/inflect.TestUnderscoreAcronymSequence: assertEqual(t, "html5_html_api", Underscore("HTML5HTMLAPI"))
        /usr/local/go/src/pkg/testing/testing.go:391 (0x3269b)
            tRunner: test.F(t)
        /usr/local/go/src/pkg/runtime/proc.c:1394 (0x180e0)
            goexit: runtime·goexit(void)
--- FAIL: TestUnderscore (0.00 seconds)
    inflect_test.go:12: inflect: expected html_tidy got h_t_m_l_tidy 
         /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:12 (0x3d546)
            com/segmentio/inflect.assertEqual: t.Errorf("inflect: expected %v got %v \n %s", a, b, debug.Stack())
        /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:448 (0x3e6f9)
            com/segmentio/inflect.TestUnderscore: assertEqual(t, underscore, Underscore(camel))
        /usr/local/go/src/pkg/testing/testing.go:391 (0x3269b)
            tRunner: test.F(t)
        /usr/local/go/src/pkg/runtime/proc.c:1394 (0x180e0)
            goexit: runtime·goexit(void)
    inflect_test.go:12: inflect: expected html_tidy_generator got h_t_m_l_tidy_generator 
         /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:12 (0x3d546)
            com/segmentio/inflect.assertEqual: t.Errorf("inflect: expected %v got %v \n %s", a, b, debug.Stack())
        /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:448 (0x3e6f9)
            com/segmentio/inflect.TestUnderscore: assertEqual(t, underscore, Underscore(camel))
        /usr/local/go/src/pkg/testing/testing.go:391 (0x3269b)
            tRunner: test.F(t)
        /usr/local/go/src/pkg/runtime/proc.c:1394 (0x180e0)
            goexit: runtime·goexit(void)
    inflect_test.go:12: inflect: expected html got h_t_m_l 
         /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:12 (0x3d546)
            com/segmentio/inflect.assertEqual: t.Errorf("inflect: expected %v got %v \n %s", a, b, debug.Stack())
        /Users/tj/dev/src/github.com/segmentio/inflect/inflect_test.go:448 (0x3e6f9)
            com/segmentio/inflect.TestUnderscore: assertEqual(t, underscore, Underscore(camel))
        /usr/local/go/src/pkg/testing/testing.go:391 (0x3269b)
            tRunner: test.F(t)
        /usr/local/go/src/pkg/runtime/proc.c:1394 (0x180e0)
            goexit: runtime·goexit(void)

I'll try and patch soon and send over a PR