[ci] Set bob doc server

.travis.yml

@@ -7,6 +7,8 @@ env:
 matrix:
   include:
   - python: 2.7
+    env:
+    - BOB_DOCUMENTATION_SERVER=https://www.idiap.ch/software/bob/docs/latest/bioidiap/%s/master
   - python: 3.3
   - python: 3.4
   - python: 3.5