fix: golangci-lint issues in tools/configtxlator

Fix some golangci-lint issues in **tools/configtxlator** file. I plan on fixing them but have some doubt regarding some of the linter errors.

1) " err = http.Serve(listener, rest.NewRouter()) " (line 127 and 130 ) wouldnt it be better to create an http.Server and set a timer for requests or is timer no required. Also instead of giving a listener could use server.ListenAndServe()

2) is the nil check required in line 236 as update.Compute only returns nil if error exists and that is already checked before

3) The command line commands (line 45-70) cause linter errors for exceeding line length limit. Should it be addressed as it doesnt look that big of an issue and spitting it in multiple lines personally looks worse to me.