Specify clear version numbers for pep8
Specify clear version numbers for pep8

and coverage and coveralls. New updates to pep8 are messing the tests
for no (really) good reason. Better to specify the version number and
explicitly upgrade when I have the time than to have tests suddenly fail
for no reason.

eusoubrasileiro/fatiando,eusoubrasileiro/fatiando_seismic,eusoubrasileiro/fatiando,santis19/fatiando,drandykass/fatiando,mtb-za/fatiando,victortxa/fatiando,eusoubrasileiro/fatiando,rafaelmds/fatiando,cmeessen/fatiando,cmeessen/fatiando,drandykass/fatiando,rafaelmds/fatiando,santis19/fatiando,eusoubrasileiro/fatiando_seismic,victortxa/fatiando,fatiando/fatiando,fatiando/fatiando,mtb-za/fatiando