TST: install cython from pip for 3.6_NUMPY_DEV build

[jreback]

No description provided.

[jreback]

@TomAugspurger seems cython released 0.27.0, its working for me locally but seems to break: https://travis-ci.org/MacPython/pandas-wheels/jobs/279039062

[codecov]

Codecov Report

Merging #17657 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17657      +/-   ##
==========================================
- Coverage   91.26%   91.22%   -0.05%     
==========================================
  Files         163      163              
  Lines       49806    49806              
==========================================
- Hits        45455    45434      -21     
- Misses       4351     4372      +21

Flag	Coverage Δ
#multiple	89.01% <ø> (-0.03%)	⬇️
#single	40.3% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/plotting/_converter.py	63.38% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.73% <0%> (-0.1%)	⬇️

---

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[codecov]

Codecov Report

Merging #17657 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17657      +/-   ##
==========================================
- Coverage   91.26%   91.22%   -0.05%     
==========================================
  Files         163      163              
  Lines       49806    49806              
==========================================
- Hits        45455    45434      -21     
- Misses       4351     4372      +21

Flag	Coverage Δ
#multiple	89.01% <ø> (-0.03%)	⬇️
#single	40.3% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/plotting/_converter.py	63.38% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.73% <0%> (-0.1%)	⬇️

---

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 965c1c8...f125c17. Read the comment docs.