Travis CI: Run each failing pytest in || true mode

Author: cclauss

.travis.yml

@@ -24,7 +24,8 @@ script:
   - pytest data_structures/stacks/balanced_parentheses.py --doctest-modules || true
   - pytest data_structures/stacks/infix_to_postfix_conversion.py --doctest-modules || true
   - pytest file_transfer_protocol/ftp_send_receive.py --doctest-modules || true
-  - pytest file_transfer_protocol/ftp_client_server.py --doctest-modules || true
+  # ftp_client_server.py currently hangs until Travis CI times out (10+ minutes)
+  # - pytest file_transfer_protocol/ftp_client_server.py --doctest-modules || true
   - pytest machine_learning/linear_regression.py --doctest-modules || true
   - pytest machine_learning/random_forest_classification/random_forest_classification.py --doctest-modules || true
   - pytest machine_learning/random_forest_regression/random_forest_regression.py --doctest-modules || true