Fix Coveralls build failure

[dzhoshkun]

After resolving #31 the Coveralls failure needs to be investigated.
@SebastianoF As far as I understand, the problem was related to Coveralls trawling through all the external dependency libraries, which was causing it to fail?

[dzhoshkun]

This line is important.

[dzhoshkun]

@SebastianoF The --cover-package bruker2nifti argument restricts coverage stats to the bruker2nifti package only.
But that argument is not enabled in your .travis.yml

See my coveralls output: https://coveralls.io/github/dzhoshkun/bruker2nifti

[SebastianoF]

Hi! Thanks for checking (in the week end counts twice!).
Yep, flags are to be refactored. They are in this state awaiting for me understand a bit more how to use properly travis-CI + coveralls. Your suggestions provided me good starting points for this direction!

[SebastianoF]

Due to the recent discoveries about orientation (see issues #11 and #33), it seems that the user will always need a small amount manual adjustment for the conversion. Therefore a 100% coverage may be more an hindrance than an help.
Increasing the coverage for the core and utils modules can still be done, although if you agree, this repo may keep on surviving without coverall for the moment.