Auspice map scroll behavior broken

[jameshadfield]

Current Behavior

In nextstrain.org when you mousewheel-scroll while the cursor is over the map we zoom into the map (no keys are pressed for this to happen). In auspice, an overlay appears over the map instructing you to "command+scroll to zoom". The exact message will differ depending on OS and comes from this leaflet plugin.

Expected behavior

Nextstrain.org should behave like auspice here -- scrollwheel with no key pressed should scroll the page, not zoom the map, and the map overlay should appear.

How to reproduce
Steps to reproduce the current behavior:

1. Open / run nextstrain.org/zika
2. Position the mouse over the map
3. Use the scroll-wheel / trackpad to scroll

Your environment

• Browser: Firefox 81.0, Safari 13.1.2
• Version: Auspice 2.18.3 (works when vanilla auspice, broken when part of nextstrain.org)
• Locally-running nextstrain.org server behaves the same as live nextstrain.org

[jameshadfield]

This is caused by an updated leaflet library in nextstrain.org which was incompatible with the leaflet-gesture-handling plugin we were using (see elmarquis/Leaflet.GestureHandling#58).

Auspice is using leaflet version 1.6.0 (as per the package-lock, package.json specifies "^1.6.0").

Nexstrain.org's package-lock specified 1.7.1 (pulled in via auspice's package.json I think). This happened inadvertently on this commit because auspice didn't pin the version of leaflet tightly enough.

Downgrading nextstrain.org's leaflet library to 1.6.0 fixes this, however the best route for this is to pin versions of leaflet / leaflet-gesture-handling in auspice.