Travis CI: don't pass -l to dump

The help text for pokedex dump -l says

    -l LANGS, --langs LANGS
                        comma-separated list of language codes to load,
                        'none', or 'all' (default: en)

However, the values 'none' and 'all' don't work (they are treated as
language names) and the default is to dump all languages, not just
English.

So `dump -l all` actually dumps no text at all because there is no
language called 'all'.

This is about to cause trouble for Travis CI because the next commit
will start checking that load/dump successfully round-trips... which
definitely isn't the case right now because the dump is missing
all text from translated tables.

The dump command and its documentation should definitely be fixed at
some point, but for now just stop using -l.

.travis.yml

@@ -13,4 +13,4 @@ install: pip install -e .
 before_script: pokedex setup -v
 script:
     - py.test
-    - pokedex dump -l all
+    - pokedex dump