Fix cargo make package (#156)

- Missing exec
- Needs to run a different command depending on whether flags are passed.
  This is different to cargo publish, which ignores trailing whitespace
  when flags are empty.

(cherry picked from commit c2ad7d2)

Author: russcam

Makefile.toml

@@ -193,7 +193,11 @@ script = [
 """
 cd elasticsearch
 echo "packaging elasticsearch crate: cargo package %{CARGO_MAKE_CARGO_PACKAGE_FLAGS}"
-cargo package %{CARGO_MAKE_CARGO_PACKAGE_FLAGS}
+if is_empty %{CARGO_MAKE_CARGO_PACKAGE_FLAGS}
+    exec cargo package
+else
+    exec cargo package %{CARGO_MAKE_CARGO_PACKAGE_FLAGS}
+end
 """
 ]