Update transifex-client used in CI build

The version we are currently using is out of date, and the Transifex API
has changed to use API keys instead of username and password.

.travis.yml

 
 env:
   global:
-    # $TRANSIFEX_PASSWORD for oscar_bot (used in transifex.sh)
-    - secure: FuIlzEsGJiAwhaIRBmRNsq9eXmuzs25fX6BChknW4lDyVAySWMp0+Zps9Bd0JgfFYUG3Ip+OTmksYIoTUsG25ZJS9cq1IFt3QKUAN70YCI/4ZBLeIdICPEyxq+Km179+NeEXmBUug17RLMLxh3MWfO+RKUHK9yHIPNNpq0dNyoo=
+    # $TRANSIFEX_PASSWORD - Transifex API key (used in transifex.sh)
+    - secure: fFOuN7cZxN74zVN6tkxwr9Kby4qxC0AxV+jvcT5HVaQ1sSl0L5SxRA7EzgCSTbkz3QjCVFrQfEvGflqTWCFqtF4ou2S9ip7Nhhs+TjsDqErhyAOodqwacp0DSzjlvPBx7AVyajdzV9iHtHrcLHyS9v5aaeCGQ4RXIqRntcM4l/c=
 
     # These two environment variables could be set by Travis itself, or Travis
     # could configure itself in /etc/, ~/, or inside of the virtual

transifex.sh

 then
     echo "Submitting translation files to Transifex"
     make messages
-    pip install "transifex-client==0.10"
+    pip install "transifex-client>=0.13,<0.14"
     # Write .transifexrc file
     echo "[https://www.transifex.com]
+api_hostname = https://www.transifex.com
 hostname = https://www.transifex.com
 password = $TRANSIFEX_PASSWORD
-token = 
-username = oscar_bot" > ~/.transifexrc
+username = api" > ~/.transifexrc
     tx push --source --no-interactive
 fi