Clean up some JavaScript quirks.
Clean up some JavaScript quirks.

- Turn on strict mode.
- Add missing semicolon.
- Eliminate check for minutes != 0 (dividing 0 is a safe operation).
- Eliminate unused `result` variable.
- Remove array initialization, it's never used.
- Replace !=null test with simple truthyness check.

Mostly because I'm customed to running JSHint while development
to report me of possible problems, but it's of no use when the
whole code shows up underlined.

toomasr/jira-calculate-hours