ENH: enable Travis to run shellcheck

[yarikoptic]

#11 could either adopt it (if we merge it in) to run shellcheck on all script/* files (all bash ATM) or we could do that later.

[yarikoptic]

I was not 100% certain that separating this way wouldn't cause some values to be interpreted as options to echo, but seems to be not:

$> cat /tmp/checkecho
#!/bin/bash
echo -e "I1: $@"
echo -e "I2:" "$@"

$> /tmp/checkecho '-n' 1 "2 3" '&' '${var}'
I1: -n 1 2 3 & ${var}
I2: -n 1 2 3 & ${var}

so all good

[yarikoptic]

ok, all green! from now on could only get even greener ;-)