Make test assertions match the test name more closely

This updates
test_editable_vcs_install_in_pipfile_with_dependency_resolution_doesnt_traceback
to check (a) that dependency resolution was triggered, and (b) that
there was no traceback (rather than just the specific traceback we are
currently seeing).

tests/test_pipenv.py

@@ -456,8 +456,8 @@ requests = {git = "https://github.com/requests/requests.git", editable = true}
                 f.write(contents)
             c = p.pipenv('install')
             assert c.return_code == 1
-            assert 'FileNotFoundError' not in c.out
-            assert 'FileNotFoundError' not in c.err
+            assert "Your dependencies could not be resolved" in c.err
+            assert 'Traceback' not in c.err
 
 
     @pytest.mark.run