Enable dupword, unconvert linters

[alexandear]

❯ golangci-lint run
bytesconv_test.go:40:18: unnecessary conversion (unconvert)
        expect := string(html.EscapeString(string(allcases)))
                        ^
fs.go:873:28: unnecessary conversion (unconvert)
        ff, ok := fileCache[string(path)]
                                  ^
fs.go:1597:16: unnecessary conversion (unconvert)
        r := io.Reader(f)
                      ^
client.go:1479:3: Duplicate words (d2) found (dupword)
                //  0(not set)            d2            d2
                ^
client.go:1481:3: Duplicate words (d2) found (dupword)
                //  0(not set)            d2            d2
                ^
http_test.go:3025:9: Duplicate words (size) found (dupword)
                t.Run("limit response body size size", func(t *testing.T) {
                      ^

[erikdubbelboer]

Thanks!