avoid '# ' <-- extra space after comment character in license headers

The current logic for inserting comments before the license description in file headers will produce "# " (notice the extra space after the comment) for empty lines in the license description.

This means that newly minted cookbook fails rubocop right out of the gate (there are actually a few other failures as well, but this one seems like low hanging fruit).

Rubocop throws the following complaint:
```
recipes/default.rb:12:2: C: Trailing whitespace detected.
# 
 ^
```

This change yields the same output (visually), but avoids the trailing space after the comment character.