Update: better operator regex in use-isnan rule (fixes #1551)

Fixes #1551.
Merge pull request #1552 from michaelficarra/patch-9

Update: better operator regex in use-isnan rule (fixes #1551)
Rule: space-after-function-name (fixes #1340)

Adds a new rule, `space-after-function-name`, that enforces
consistent spacing between a function name and its parameters.