'sep' is not used by the print fixer

Should raise coverage of fix_print to 100%
Drop a check in fix_next for an empty base

Since the matching rule is `base+` there will have to be a match for
something.

Should make coverage for fix_next 100%.
add tests for fix_map

Along the way discover an unnecessary limitation in the pattern.
test fix_map w/ kwargs
Rename a test to make its purpose more obvious
Add test_fix_filter

Along the way fix the pattern from being too broad (filter only accepts
2 arguments).
Add tests for fix_zip

Discovered the pattern was too restrictive in some senses — e.g. didn’t
allow for the empty call which is legal — and too loose — e.g. allowed
for keyword arguments.
add tests for fix_raise
Add tests for fix_metaclass

Include a fix for the one-liner case.
Tests for fix_dict
Add a test for `zip(*args)`
Merge pull request #46 from brettcannon/increase_coverage

Increase test coverage