text: Title: Improve test coverage from 91% to 100%
  Body: Test coverage is always important, and my goal is to eventually be at 100%. I'll be sure to do this for PRs from now on, or at least try to, but there is some existing code that is not yet covered.
  
  The good thing is that all files have existing tests, tests for `__main__.py` for example can be found in the [`main_test.py`](https://github.com/python-security/pyt/blob/master/tests/main_test.py) file.
  
  By running `make test` you can see where we aren't yet at 100%:
  
  ```python
  py36 runtests: commands[3] | coverage report --include=pyt/* --fail-under 91
  Name                                                Stmts   Miss  Cover   Missing
  ---------------------------------------------------------------------------------
  pyt/__init__.py                                         0      0   100%
  pyt/__main__.py                                        68     13    81%   45, 55-57, 70-71, 83, 86, 105-108, 129
  pyt/analysis/constraint_table.py                        9      0   100%
  pyt/analysis/definition_chains.py                      16      0   100%
  pyt/analysis/fixed_point.py                            21      0   100%
  pyt/analysis/lattice.py                                31      0   100%
  pyt/analysis/reaching_definitions_taint.py             27      0   100%
  pyt/cfg/__init__.py                                     2      0   100%
  pyt/cfg/alias_helper.py                                33      0   100%
  pyt/cfg/expr_visitor.py                               212     20    91%   70, 99-100, 111-122, 131, 136, 141, 149, 154, 407, 560
  pyt/cfg/expr_visitor_helper.py                          9      0   100%
  pyt/cfg/make_cfg.py                                     9      0   100%
  pyt/cfg/stmt_visitor.py                               456     46    90%   111, 168, 174, 217, 235, 247-248, 277-278, 297-298, 386-399, 658-661, 668-671, 678, 684, 702-704, 780, 816-823, 868, 893, 919-920, 951, 972, 988, 1010
  pyt/cfg/stmt_visitor_helper.py                         72      6    92%   83, 95-96, 133-136
  pyt/core/ast_helper.py                                 53      4    92%   56, 101, 103, 105
  pyt/core/module_definitions.py                         47      4    91%   32, 108-110
  pyt/core/node_types.py                                 70      4    94%   51, 142-145
  pyt/core/project_handler.py                            30      1    97%   23
  pyt/formatters/__init__.py                              0      0   100%
  pyt/helper_visitors/__init__.py                         4      0   100%
  pyt/helper_visitors/label_visitor.py                  206     40    81%   31-37, 93-98, 179-184, 186-188, 200, 203, 212, 215, 218, 221, 224, 227, 230, 246, 249, 252, 255, 261, 265, 271, 274, 278, 281
  pyt/helper_visitors/right_hand_side_visitor.py         13      0   100%
  pyt/helper_visitors/vars_visitor.py                   104      4    96%   66-68, 102
  pyt/usage.py                                           39      1    97%   124
  pyt/vulnerabilities/__init__.py                         3      0   100%
  pyt/vulnerabilities/trigger_definitions_parser.py      30      0   100%
  pyt/vulnerabilities/vulnerabilities.py                160     15    91%   233-235, 237, 241-243, 310, 312-321, 424, 427
  pyt/vulnerabilities/vulnerability_helper.py            76     19    75%   84, 116-119, 132-134, 178-182, 204-209
  pyt/web_frameworks/__init__.py                          3      0   100%
  pyt/web_frameworks/framework_adaptor.py                41      0   100%
  pyt/web_frameworks/framework_helper.py                 23      0   100%
  ---------------------------------------------------------------------------------
  TOTAL                                                1867    177    91%
  ```
  
  If you would like help with writing tests for any of these files let me know.