Using Webstorm->Preferences->Editor->Code Style->JavaScript Use semicolon to terminate spaces works fine for me. Maybe double check what Code Style scheme you are setting that for. Sometimes I have changed code style settings, but for a different scheme than the one being applied to the project in question.
Placing caret on problematic place in your Editor and bringing Quick Fix menu (Alt + Enter or by clicking on light bulb icon)
Choosing right option in appeared menu (if not sure which one then try step #3 for few of them)
Arrow Right (or click on small triangle on the right side) to open submenu
Choose desired action
P.S.
JSLinh/JSHint and alike may also produce such warnings if you are using these tools.
As for the actual code generated by IDE (e.g. when using Code | Reformat... or using code completion popup/functionality) -- such option is available at