Fix lint errors for flake8 v3.5.0

[drewcm]

Fixes parsedatetime lint errors for flake8 v3.5.0 (mccabe: 0.6.1, pycodestyle: 2.3.1, pyflakes: 1.6.0). Required to be fixed before tests will run. The nl_NL.py error references "different values" for 'vorige' key, but to my eye they are the same.

$ make test
flake8 parsedatetime > violations.flake8.txt
Makefile:54: recipe for target 'lint' failed
make: *** [lint] Error 1
$ cat violations.flake8.txt
parsedatetime/pdt_locales/icu.py:141:5: E741 ambiguous variable name 'l'
parsedatetime/pdt_locales/nl_NL.py:74:5: F601 dictionary key 'vorige' repeated with different values
parsedatetime/pdt_locales/nl_NL.py:80:5: F601 dictionary key 'vorige' repeated with different values
$ flake8 --version
3.5.0 (mccabe: 0.6.1, pycodestyle: 2.3.1, pyflakes: 1.6.0) CPython 3.5.2 on Linux
$ git rev-parse HEAD
830775dc5e36395622b41f12317f5e10c303d3a2

Link to code in question:

• parsedatetime/parsedatetime/pdt_locales/icu.py

  Line 141 in 830775d

  l = s.lower().split(ds)

• parsedatetime/parsedatetime/pdt_locales/nl_NL.py

  Line 74 in 830775d

  'vorige': -1,

• parsedatetime/parsedatetime/pdt_locales/nl_NL.py

  Line 80 in 830775d

  'vorige': -1,

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This change is