upgraded mypy to 0.782

This upgraded mypy version detects additional issues which were
ignored in the previous versions.

Additionally, mypy 0.782 is compatible with Python 3.8 (which we want to
upgrade to eventually).

icontract_lint/__init__.py

@@ -496,12 +496,14 @@ def check_file(path: pathlib.Path) -> List[Error]:
         cause = err.__cause__
         assert isinstance(cause, SyntaxError)
 
+        lineno = -1 if cause.lineno is None else cause.lineno  # pylint: disable=no-member
+
         return [
             Error(
                 identifier=ErrorID.INVALID_SYNTAX,
                 description=cause.msg,  # pylint: disable=no-member
                 filename=path.as_posix(),
-                lineno=cause.lineno)  # pylint: disable=no-member
+                lineno=lineno)  # pylint: disable=no-member
         ]
 
     lint_visitor = _LintVisitor(filename=path.as_posix())

setup.py

@@ -43,7 +43,7 @@
     extras_require={
         'dev': [
             # yapf: disable
-            'mypy==0.620',
+            'mypy==0.782',
             'pylint==2.6.0',
             'yapf==0.20.2',
             'tox>=3.0.0',