TST: codecov.yml improvements

* we no longer require CircleCI jobs
to pass for coverage reporting, and
failures of Travis jobs other than
the single coverage job should not
interfere with coverage reporting now

.codecov.yml

@@ -1,6 +1,22 @@
 codecov:
   ci:
+    # we don't require appveyor or
+    # circleCI to pass to report
+    # coverage, which currently only
+    # comes from a single Python 3.6 job
+    # in Travis
     - !appveyor
+    - !circle
+  notify:
+    # don't require all travis builds to pass;
+    # as long as the coverage job succeeds it
+    # can report the % coverage, even if another
+    # job needs a restart for whatever reason
+    - require_ci_to_pass: no
+    # we should only require a single build before
+    # reporting the % coverage because there's only
+    # one coverage job in Travis
+    - after_n_builds: 1
 coverage:
   status:
     project: