app.js: update searchdata URL in prep for format change
app.js: update searchdata URL in prep for format change

The new URL is:

http://worldwidetelescope.org/data/searchdata_v2.min.js

(or https://, or `cdn.worldwidetelescope.org`, etc.)

WorldWideTelescope/wwt-web-client,WorldWideTelescope/wwt-web-client