Fix reference to no-longer-existent 'rollup.config.js' file (#544)

ExplodingCabbage · web-flow · commit 739bfff946e8 · 2024-08-20T17:51:27.000+01:00
Should've been done as part of #505, but I missed it
diff --git a/.npmignore b/.npmignore
@@ -10,7 +10,7 @@ Gruntfile.js
 images
 index.html
 karma.conf.js
-rollup.config.js
+rollup.config.mjs
 src
 tasks
 test
