Fix looking for description in wrapped gulp task function

[daanporon]

Gulp task functions are wrapped inside a wrapper function … unwrap the tasks first to look for the description.

https://github.com/gulpjs/undertaker/commit/67fd02cdc217326cab2aa3d1d7be ca9ea12cfde6

[akrawchyk]

@chmontgomery without this change I don't see descriptions or flags in the help output