Add transformer for request.xreadlines()

[browniebroke]

Removed in Django 3.0:

HttpRequest.xreadlines() will be removed.

Deprecated since Django 2.0:

HttpRequest.xreadlines() is deprecated in favor of iterating over the request.

Fixes #52

[codecov]

Codecov Report

Merging #199 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #199   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines          639       649   +10     
=========================================
+ Hits           639       649   +10     

Impacted Files	Coverage Δ
django_codemod/visitors/__init__.py	100.00% <ø> (ø)
django_codemod/visitors/http.py	100.00% <100.00%> (ø)

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[sourcery-ai]

Sourcery Code Quality Report

This PR has an average code quality of 88.49%

Quality metrics	Before	After	Change
Complexity		0.06 ⭐
Method Length		34.18 ⭐
Working memory		7.39 🙂
Quality	%	88.49% ⭐	%

Other metrics	Before	After	Change
Lines		504

Changed files	Quality Before	Quality After	Quality Change
django_codemod/visitors/init.py	%	56.77% 🙂	%
django_codemod/visitors/http.py	%	86.86% ⭐	%
tests/test_cli.py	%	85.87% ⭐	%
tests/visitors/test_http.py	%	96.19% ⭐	%

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
tests/test_cli.py	test_deprecated_in_mapping	0	67 🙂	38 ⛔	57.66% 🙂	Extract out complex expressions
tests/test_cli.py	test_removed_in_mapping	0	59 ⭐	36 ⛔	59.00% 🙂	Extract out complex expressions
tests/test_cli.py	test_basic_arguments	1 ⭐	94 🙂	11 😞	66.94% 🙂	Extract out complex expressions
tests/test_cli.py	test_get_short_description	0	32 ⭐	11 😞	77.52% ⭐	Extract out complex expressions

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The 👍 and 👎 indicate whether the quality has improved or gotten worse with this pull request.

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