Fix window.open() looks not working
Fix window.open() looks not working

Intorduced by f8fadcb8446001bf9b303bf086b4ac01d7fd7e8d
because {show:false} option was inherited from the main window.

https://github.com/electron/electron/blob/v1.4.13/docs/api/window-open.md

Close #450

yuya-oc/desktop,yuya-oc/electron-mattermost,mattermost/desktop,jnugh/desktop,yuya-oc/desktop,jnugh/desktop,yuya-oc/electron-mattermost,mattermost/desktop,jnugh/desktop,mattermost/desktop,mattermost/desktop,yuya-oc/electron-mattermost,yuya-oc/desktop,mattermost/desktop