Fix refactoring bug from 23 october in util/exe

23 October, {} instead of #{} totally break windows service generation
https://github.com/rapid7/metasploit-framework/commit/f19b093529f3b3aacefb69f8133ab788859445d1#diff-0f5729034d8b0b321e738f2fc047854fL578
Land 4127, fix broken refactor in util/exe