Add an example of input wavelengths.

Add an example of how the input wavelengths should be passed to the NIST
query. Related to #251.
Fix example.

The example query was from 40000 Angstrons to 70000 Angstrons. I have
changed that and I have changed the output query to reflect the same as
mine.
Removed double entry in travis setup.
Merge pull request #253 from jwoillez/travis_remove_double

Removed double entry in travis setup.
Merge pull request #251 from gabraganca/NIST_example

NIST: spectral lines not showed
minor fix in NIST docs