Be more strict about which files are included in crate packaging

[lopopolo]

Without these changes, prettier metadata in node_modules is included:

$ cargo package --list --allow-dirty
.cargo_vcs_info.json
Cargo.toml
Cargo.toml.orig
LICENSE
README.md
node_modules/prettier/LICENSE
node_modules/prettier/README.md
src/format/assert.rs
src/format/check.rs
src/format/mod.rs
src/format/utils.rs
src/format/week.rs
src/format/write.rs
src/lib.rs
src/mock.rs.in
src/tests/error.rs
src/tests/format.rs
src/tests/mod.rs
tests/version_numbers.rs
vendor/README.md