chore(deps): bump ep_plugin_helpers to ^0.6.0

0.6.x is the current line on npm (latest = 0.6.2) and the prior range
doesn't resolve to it under caret semver for pre-1.0. Without this bump,
fresh installs of this plugin pull a stale ep_plugin_helpers and miss
fixes shipped in 0.6.x — including ether/ep_plugin_helpers#19 which
corrected the misleading "Etherpad < 2.7.4" degradation warning.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JohnMcLear

package.json

@@ -30,7 +30,7 @@
     "url": "https://etherpad.org/"
   },
   "dependencies": {
-    "ep_plugin_helpers": "^0.4.0",
+    "ep_plugin_helpers": "^0.6.0",
     "highlight.js": "^11.10.0"
   },
   "devDependencies": {