Fix to Issue #26

https://github.com/Esri/map-tour-storytelling-template-js/issues/26

The functions getVimeoEmbed(url) and getVimeoThumbnail(url) only worked
correctly for videos with ids of exactly 8 digits. I tested the builder
on a vimeo video with 9 digits and one with 7 digits and they both added
correctly. Before, the video with 9 digits would have matched to a video
with the first 8 digits and the video with 7 digits wouldn't have found
a thumbnail.