Make punctuation consistent

[josealberto4444]

Added some periods where missing in readme and code of conduct.

[josealberto4444]

I changed the sentence order for avoiding having the URLs with a trailing period. If you say they are valid addresses (I couldn't find the answer online, so I trust you), I don't want to trust the parser to guess right if those periods are punctuation or part of the URL.

In the code of conduct, as it is written in markdown, there was no need to fix this, so I simply let the period at the end, out of the link.

[codecov]

Codecov Report

Merging #4059 into master will decrease coverage by 2%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4059      +/-   ##
==========================================
- Coverage   85.68%   83.68%   -2.01%     
==========================================
  Files         165      165              
  Lines        9734     9713      -21     
  Branches     1463     1445      -18     
==========================================
- Hits         8341     8128     -213     
- Misses       1136     1336     +200     
+ Partials      257      249       -8

Impacted Files	Coverage Δ
scrapy/linkextractors/sgml.py	0% <0%> (-96.81%)	⬇️
scrapy/linkextractors/regex.py	0% <0%> (-95.66%)	⬇️
scrapy/linkextractors/htmlparser.py	0% <0%> (-92.07%)	⬇️
scrapy/extensions/statsmailer.py	0% <0%> (-30.44%)	⬇️
scrapy/utils/reqser.py	88.23% <0%> (-5.89%)	⬇️
scrapy/utils/python.py	80% <0%> (-4.24%)	⬇️
scrapy/utils/datatypes.py	56.61% <0%> (-3.6%)	⬇️
scrapy/linkextractors/__init__.py	96.66% <0%> (-3.34%)	⬇️
scrapy/utils/gz.py	96.87% <0%> (-3.13%)	⬇️
scrapy/utils/trackref.py	83.78% <0%> (-2.71%)	⬇️
... and 80 more

[josealberto4444]

Sorry for the delay. I didn't know I had to commit also the suggestion, I thought you could commit it on top of the pull request. I'm not very used to GitHub's pull requests, as you can see.

Thanks!

[wRAR]

@josealberto4444 to commit a suggestion one would need a write access to the repo, which only you have :)

[josealberto4444]

@josealberto4444 to commit a suggestion one would need a write access to the repo, which only you have :)

I see... Understood! =)