.travis.yml: fix test folder exclude for coveralls report
.travis.yml: fix test folder exclude for coveralls report

Coverage report should not include test/ folder.
Fixed existing but misspelled --exclude argument to achieve this.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

rauc/rauc,rauc/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,jluebbe/rauc,ejoerns/rauc,jluebbe/rauc