[build] Set default backend to 'wa' in package `wacoq`.

Quote escaping hell in this tiny `sed` script.

package.json

@@ -62,7 +62,7 @@
     "build": "webpack --mode production",
     "build:dev": "webpack",
     "watch": "webpack -w",
-    "prepack": "sed -i.bak 's/\\(is_npm:\\) false/\\1 true/' ui-js/jscoq-loader.js"
+    "prepack": "sed -i.in 's/\\(is_npm:\\) false/\\1 true/' ui-js/jscoq-loader.js"
   },
   "repository": {
     "type": "git",

package.json.wacoq

@@ -60,7 +60,7 @@
     "build": "webpack --mode production",
     "build:dev": "webpack",
     "watch": "webpack -w",
-    "prepack": "sed -i.bak 's/\\(is_npm:\\) false/\\1 true/' ui-js/jscoq-loader.js"
+    "prepack": "sed -i.in 's/\\(is_npm:\\) false/\\1 true/;s/\\(backend:\\) .*/\\1 '\\'wa\\'/ ui-js/jscoq-loader.js"
   },
   "repository": {
     "type": "git",