Minor: remove gratuitous parens around expressions
Minor: remove gratuitous parens around expressions

This has three benefits:

1. Before this change, the unminified source was 15,695 bytes.
   Afterward, it is 15,499 bytes. I suspect that there are some people
   out there who aren't minifying this library; this will save 196
   bytes. This should have no effect on minified code.

2. It's good to remove unneeded stuff.

3. ESLint will shut up about it by default.

EvanHahn/HumanizeDuration.js,smnbbrv/HumanizeDuration.js