Fix #75: Update template for stateless components

[mwolson]

The {{else if ...}} construct is not supported prior to handlebars v3.0.0. Based on yarn.lock, seems like plop is using handlebars 2.0.0.

• Replace {{else if ...}} with a nested if/else block
• Remove unnecessary branch point on {{#unless wantFlowTypes}} which will never be reached since that condition is already checked in an earlier if condition.

[RyanCCollins]

Thanks for this! The generators have been changing quite often lately. Appreciate you helping to refine them!