Code review fixes.

Author: Nurdok

src/pydocstyle/parser.py

@@ -34,7 +34,7 @@ def next(obj, default=nothing):
 
 class ParseError(Exception):
     def __str__(self):
-        return "cannot parse file"
+        return "Cannot parse file."
 
 
 def humanize(string):

src/tests/test_integration.py

@@ -974,5 +974,5 @@ def test_syntax_error_multiple_files(env):
 
     out, err, code = env.invoke(args="-v")
     assert code == 1
-    assert 'first.py: cannot parse file' in err
-    assert 'second.py: cannot parse file' in err
+    assert 'first.py: Cannot parse file' in err
+    assert 'second.py: Cannot parse file' in err