Skip gevent tests on py33

Seems to be unsupported on recent versions.

.travis.yml

@@ -8,7 +8,7 @@ matrix:
   include:
     - {python: "2.6",      env: SKIP_GEVENT=true    SKIP_DEPLOY=true}
     - {python: "2.7",      env: SKIP_GEVENT=true                    }
-    - {python: "3.3",      env:                     SKIP_DEPLOY=true}
+    - {python: "3.3",      env: SKIP_GEVENT=true    SKIP_DEPLOY=true}
     - {python: "3.4",      env:                                     }
     - {python: "3.5",      env:                     SKIP_DEPLOY=true}
     - {python: "3.6",      env:                     SKIP_DEPLOY=true}