Add help text for Node.js snap failures

The official Node.js Snap as distributed via the Ubuntu Snap Store
does not provide support for native modules.

Sometimes, if the version of the core matches the version of the
underlying OS, then it will appear to work.

There are quite a few open issues relating to this in the
nodejs/snap repo.

lib/sharp.js

@@ -77,6 +77,12 @@ if (sharp) {
       );
     } catch (errEngines) {}
   }
+  if (isLinux && /\/snap\/core[0-9]{2}/.test(messages)) {
+    help.push(
+      '- Remove the Node.js Snap, which does not support native modules',
+      '    snap remove node'
+    );
+  }
   if (isMacOs && /Incompatible library version/.test(messages)) {
     help.push(
       '- Update Homebrew:',