fix(gatsby-plugin-subfont): escape file paths (#12905)

fixes #12702

packages/gatsby-plugin-subfont/package.json

@@ -24,6 +24,7 @@
   "license": "MIT",
   "dependencies": {
     "@babel/runtime": "^7.0.0",
+    "shell-escape": "^0.2.0",
     "subfont": "^3.6.1"
   },
   "devDependencies": {

packages/gatsby-plugin-subfont/src/gatsby-node.js

@@ -1,16 +1,22 @@
 const path = require(`path`)
 const { execSync } = require(`child_process`)
+const shellescape = require(`shell-escape`)
 
 exports.onPostBuild = ({ store }) => {
   const root = path.join(store.getState().program.directory, `public`)
   // TODO make this configurable
   const urlPaths = [`/`]
-  const filePaths = urlPaths.reduce(
-    (accumulator, currentPath) =>
-      `${accumulator} ${path.join(root, currentPath, `index.html`)}`,
-    ``
+  const baseArgs = [
+    `node_modules/.bin/subfont`,
+    `-i`,
+    `--no-recursive`,
+    `--inline-css`,
+    `--root`,
+    `file://${root}`,
+  ]
+  const args = baseArgs.concat(
+    urlPaths.map(currentPath => path.join(root, currentPath, `index.html`))
   )
-
-  const command = `node_modules/.bin/subfont -i --no-recursive --inline-css --root file://${root}${filePaths}`
+  const command = shellescape(args)
   execSync(command)
 }