[upload csv to hive] fix call to unicodereader.next()

[timifasubaa]

Calling unicodeReader.next() was problematic because it works on python2 but not python3. The correct way to get the first item in the list is next(items) or for i in items. next(items) works in both python2 and 3.

@michellethomas @john-bodley

[codecov-io]

Codecov Report

Merging #4804 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #4804   +/-   ##
=======================================
  Coverage   72.34%   72.34%           
=======================================
  Files         208      208           
  Lines       15511    15511           
  Branches     1202     1202           
=======================================
  Hits        11221    11221           
  Misses       4287     4287           
  Partials        3        3

Impacted Files	Coverage Δ
superset/db_engine_specs.py	51.89% <0%> (ø)	⬆️

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[john-bodley]

@timifasubaa it seems in Python 2 uses reader.next() whereas Python 3 uses next(reader). Is this what you mean by being unreliable?

For Python 2 there is a next(reader) method however the logic differs.

[timifasubaa]

@john-bodley yes. Thanks for clarifying. I updated the PR description.
I tested on python2 and 3 and it works fine.