(chore) add file extensions in heft-plugin.json

Author: dmichon-msft

heft-plugins/heft-sass-load-themed-styles-plugin/heft-plugin.json

@@ -4,7 +4,7 @@
   "taskPlugins": [
     {
       "pluginName": "sass-load-themed-styles-plugin",
-      "entryPoint": "./lib/SassLoadThemedStylesPlugin"
+      "entryPoint": "./lib/SassLoadThemedStylesPlugin.js"
     }
   ]
 }

heft-plugins/heft-sass-plugin/heft-plugin.json

@@ -4,7 +4,7 @@
   "taskPlugins": [
     {
       "pluginName": "sass-plugin",
-      "entryPoint": "./lib/SassPlugin"
+      "entryPoint": "./lib/SassPlugin.js"
     }
   ]
 }