List build-essential as one of the `build-packages` for gtk parts (#147)
List build-essential as one of the `build-packages` for gtk parts (#147)

Avoid `make: gcc: Command not found` error when the including snap
doesn't require a GCC toolchain by itself.

Fixes #146.

Refer-to: gtk3 part doesn't install gcc · Issue #146 ·
ubuntu/snapcraft-desktop-helpers
<https://github.com/ubuntu/snapcraft-desktop-helpers/issues/146>
Signed-off-by: 林博仁(Buo-ren, Lin) <e1a755dad2798d70422023dceee1245c3d6b4517@gmail.com>
ubuntu/snapcraft-desktop-helpers