perf(spread/pips): use a buffer and use innerHTML only once
perf(spread/pips): use a buffer and use innerHTML only once

Before (test page): between 2 and 5 ms
After (test page): less than 1ms

leongersen/noUiSlider,leongersen/noUiSlider,leongersen/noUiSlider,leongersen/noUiSlider