Don't use zope-testrunner -j99 from tox or travis

That doesn't work, just causes all but one of the functional test layers
to be silently skipped (thanks to zopefoundation/zope.testrunner#5 and
zopefoundation/zope.testrunner#6).

.travis.yml

@@ -9,6 +9,6 @@ install:
     - travis_retry pip install -e .
 script:
     - zope-testrunner -u --test-path=src --auto-color --auto-progress
-    - zope-testrunner -f -j99 --test-path=src --auto-color --auto-progress
+    - zope-testrunner -f --test-path=src --auto-color --auto-progress
 notifications:
     email: false

tox.ini

@@ -6,7 +6,7 @@ commands =
 # Run unit tests first.
     zope-testrunner -u --test-path=src --auto-color --auto-progress
 # Only run functional tests if unit tests pass.
-    zope-testrunner -f -j99 --test-path=src --auto-color --auto-progress
+    zope-testrunner -f --test-path=src --auto-color --auto-progress
 # without explicit deps, setup.py test will download a bunch of eggs into $PWD
 deps =
     BTrees