Drop dependency on deprecated gulp-util

[demurgos]

Closes #14

[demurgos]

chalk@2 fails on older Node versions. Using chalk@1 can fix this.

[about-code]

@demurgos I'd say the versions of node used in the travis-ci build have little relevance anymore and could be ignored in favour of chalk@2.

@joakimbeng would you mind accept this PR? Its an important contribution and would keep gulp-conflict usable with upcoming gulp 4. It would also resolve some issues I had with gulp-conflict on windows machines due to its dependency on gulp-util and thus its transitive dependency on the beeper module.

[about-code]

See also slushjs/slush/issues/26