BUG: Using categorical dtype in read_json

[anki-code]

Pandas read_json ignores category dtype. This fix is need to using category in read_json.
Example: pd.read_json(filename, lines=True, dtype={'ColumnName':'category'}).

fyi #21892

[pep8speaks]

Hello @anki-code! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-03-06 18:11:31 UTC

[WillAyd]

This needs tests - should always be the first part of any PR

[codecov]

Codecov Report

Merging #25573 into master will decrease coverage by 49.54%.
The diff coverage is 33.33%.

@@             Coverage Diff             @@
##           master   #25573       +/-   ##
===========================================
- Coverage   91.26%   41.71%   -49.55%     
===========================================
  Files         173      173               
  Lines       52966    52968        +2     
===========================================
- Hits        48337    22096    -26241     
- Misses       4629    30872    +26243

Flag	Coverage Δ
#multiple	?
#single	41.71% <33.33%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/json/json.py	62.79% <33.33%> (-30.44%)	⬇️
pandas/io/formats/latex.py	0% <0%> (-100%)	⬇️
pandas/core/categorical.py	0% <0%> (-100%)	⬇️
pandas/io/sas/sas_constants.py	0% <0%> (-100%)	⬇️
pandas/tseries/plotting.py	0% <0%> (-100%)	⬇️
pandas/tseries/converter.py	0% <0%> (-100%)	⬇️
pandas/io/formats/html.py	0% <0%> (-99.36%)	⬇️
pandas/core/groupby/categorical.py	0% <0%> (-95.46%)	⬇️
pandas/io/sas/sas7bdat.py	0% <0%> (-91.17%)	⬇️
pandas/io/sas/sas_xport.py	0% <0%> (-90.15%)	⬇️
... and 131 more

---

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 3e652ac...e3bb759. Read the comment docs.

[codecov]

Codecov Report

Merging #25573 into master will decrease coverage by <.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master   #25573      +/-   ##
==========================================
- Coverage   91.26%   91.25%   -0.01%     
==========================================
  Files         173      173              
  Lines       52966    52968       +2     
==========================================
+ Hits        48337    48338       +1     
- Misses       4629     4630       +1

Flag	Coverage Δ
#multiple	89.83% <66.66%> (-0.01%)	⬇️
#single	41.71% <33.33%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/json/json.py	93.02% <66.66%> (-0.21%)	⬇️

---

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 3e652ac...e3bb759. Read the comment docs.