fix: don't send all files in header

[mrexox]

Closes https://github.com/coverallsapp/coverage-reporter/issues/80

:zap: Summary

We were passing all files in a header, so its size was about 20Kb, which is not acceptable.

:ballot_box_with_check: Checklist

• [x] Add specs

[coveralls-official[bot]]

Pull Request Test Coverage Report for Build 5142844652

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.085%

---

Totals
Change from base Build 5111119136:	0.0%
Covered Lines:	745
Relevant Lines:	827

---

💛 - Coveralls