Remove "enum34" requirement in setup.py.

[Freso]

The enum module is not actually imported in any part of the codebase and "enum34" isn't relevant for Python version 3.4 and later even if it was relevant. (Current Python is 3.6.x.)

freso@koume /t/f/concierge (master)> git grep -i enum|cat
concierge/core/lexer.py:    for index, line in enumerate(lines, start=1):
setup.py:    "enum34"

[Freso]

Tests for Python 3.3 and 3.4 are failing because some of the dependencies for testing require Python ≥ 3.5…