fix the attrs version and http proxy

[Yyonging]

1.the attrs lib is not compatible， and most people will use the 19.3.0 version. so theconvert has been change to converter. the attrs author may think the compatible is not so good....
2. the http proxy setting takes no effect if the proxy is http://127.0.0.1:1080 or the other http proxy.

[codecov]

Codecov Report

Merging #5 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master       #5   +/-   ##
=======================================
  Coverage   98.65%   98.65%           
=======================================
  Files          12       12           
  Lines         522      522           
=======================================
  Hits          515      515           
  Misses          7        7           

Impacted Files	Coverage Δ
aiograph/types/__init__.py	100.00% <ø> (ø)
aiograph/api.py	100.00% <100.00%> (ø)
aiograph/types/page_list.py	100.00% <100.00%> (ø)

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[Rongronggg9]

Any plan to release a new version to PyPI?