Update clean part of Makefile
Fix makefile
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Updated Makefile related to https://github.com/lcolladotor/derfinderHelper/commit/54a972165101391c0ad6d43491bf351b6416d0ba
Fixed test error foudn in https://travis-ci.org/lcolladotor/derfinder/builds/36299160
Fixed double use of the 'chrs' argument in coverageToExon() when fullCov=NULL