Test py38 instead of py36 on CircleCI

[my8100]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 393

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.05%) to 87.872%

---

Files with Coverage Reduction	New Missed Lines	%
scrapydweb/views/dashboard/jobs.py	2	91.14%

Totals
Change from base Build 356:	-0.05%
Covered Lines:	3514
Relevant Lines:	3999

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #124 into master will decrease coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #124      +/-   ##
==========================================
- Coverage   89.22%   89.17%   -0.06%     
==========================================
  Files          34       34              
  Lines        3999     3999              
==========================================
- Hits         3568     3566       -2     
- Misses        431      433       +2

Impacted Files	Coverage Δ
scrapydweb/views/files/log.py	95.02% <0%> (-0.53%)	⬇️