i use a webpack setup that balks loudly when this happens

i think v3.4.1 changed rollup plugin for typescript builds which might have caused this

possible fix

diff --git a/package.json b/package.json
index c12de53..42be4ee 100644
--- a/package.json
+++ b/package.json
@@ -47,7 +47,8 @@
     "./dist/purify.js": "./dist/purify.js"
   },
   "files": [
-    "dist"
+    "dist",
+    "src"
   ],
   "xo": {
     "semicolon": true,

there may be other alternatives also such as not publishing source maps. I often just do that though (include src)