ibu: replace ~~ with Math.trunc in res.length (option)

[tpscrpt]

#1275 is fixed by this, though this implementation probably shouldn't be merged into master it can benefit whoever was suffering from the content length being too large to be notnoted.

[tpscrpt]

test.js:

const { response } = require('./context.js')

res = response()
res.body = "Testing purposes, the average payload is most likely much larger than this; therefore some extra padding was added during the creation of this magnificent sentence."

const start = Date.now()

for(let i = 0; i < 100000000; i ++) {
  let temp = res.length
}

const diff = Date.now() - start
console.log(res.length)
console.log(diff / 1000)

[codecov]

Codecov Report

Merging #1288 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #1288   +/-   ##
======================================
  Coverage     100%    100%           
======================================
  Files           5       5           
  Lines         393     393           
======================================
  Hits          393     393

Impacted Files	Coverage Δ
lib/response.js	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 48993ad...f5d3640. Read the comment docs.

[dead-horse]

Math.trunc(len) || 0 to avoid NaN