make _close_process exception for human

[sunhailin-Leo]

• make function _close_process exception hints for human 😄

[codecov-io]

Codecov Report

Merging #225 into dev will decrease coverage by 0.09%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##              dev     #225     +/-   ##
=========================================
- Coverage   92.38%   92.29%   -0.1%     
=========================================
  Files          48       48             
  Lines        7105     7108      +3     
=========================================
- Hits         6564     6560      -4     
- Misses        541      548      +7

Impacted Files	Coverage Δ
pyppeteer/launcher.py	87.75% <0%> (-1.37%)	⬇️
tests/test_frame.py	96.53% <0%> (-0.65%)	⬇️
pyppeteer/network_manager.py	92.1% <0%> (-0.27%)	⬇️

---

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 56f8710...0526ee6. Read the comment docs.