Bug fix help.hbs

Removing extra curly bracket in `data-term="{{term}}"`, causing error on `grunt init`. Error code:

    Running "assemble:docsDev" (assemble) task
    Assembling docs/dev/index.html ERROR
    Warning: Parse error on line 6:
    ...e" data-term="{{term}}}">close</button>
    -----------------------^
    Expecting 'CLOSE', got 'CLOSE_UNESCAPED' Use --force to continue.
    
    Aborted due to warnings.