[BUGFIX] Add support for multiple -i args for cover command

[golyshevd]

Hi! istanbul cover does not support multiple -i arguments, because glob used incorrectly

istanbul cover -i "express/**/*.js" node_modules/.bin/_mocha
#ok, report written to disk

istanbul cover -i "express/**/*.js" -i "utils/**/*.js" node_modules/.bin/_mocha
#no coverage information collected

[coveralls]

Coverage decreased (-0.07%) to 97.454% when pulling aed0465 on golyshevd:fix-cover into 89e338f on gotwarlost:master.

[golyshevd]

ping! :(