resolve symlink during copy for helm package

symlinks inside the chart folder would be copied to the new directory
for package. If those symlinks are relative, they wouldn't resolve
  anymore in the new location.

Calling cp with `-L` should resolve the symlinks before copying.

helm-git-plugin.sh

@@ -178,7 +178,7 @@ helm_package() {
   helm_args=${helm_args:-}
 
   tmp_target="$(mktemp -d "$TMPDIR/helm-git.XXXXXX")"
-  cp -r "$_source_path" "$tmp_target/$_chart_name"
+  cp -rL "$_source_path" "$tmp_target/$_chart_name"
   _source_path="$tmp_target/$_chart_name"
   cd "$_target_path" >&2