Travis: use codecov-bash

More lightweight to install, and will retry on upload failures.

Author: blueyed

.travis.yml

@@ -37,8 +37,11 @@ script:
   - tox
 
 after_success:
-  - pip install codecov
-  - codecov
+  # Upload coverage information for py* tox environments.
+  - |
+    if [ "${TOXENV#py}" != "$TOXENV" ]; then
+      bash <(curl -s https://codecov.io/bash) -Z -F "${TOXENV//-/,}"
+    fi
 
 branches:
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