Normalise line endings when patching user files

We want to make sure that on Windows we can compare files regardless of
what line endings the users files have, and that any changes we make
have the same line endings.

lib/_update/util/index.js

@@ -11,9 +11,21 @@ async function getProjectVersion () {
 }
 
 async function patchUserFile (originalVersion, filePath) {
-  const original = await fetchOriginal(originalVersion, filePath)
   const theirs = await fs.readFile(path.resolve(projectDir, filePath), 'utf8')
-  const ours = await fs.readFile(path.resolve(updateDir, filePath), 'utf8')
+  let original = await fetchOriginal(originalVersion, filePath)
+  let ours = await fs.readFile(path.resolve(updateDir, filePath), 'utf8')
+
+  // normalise line endings
+  var eol = '\n'
+  if (theirs.includes('\r\n')) {
+    eol = '\r\n'
+    if (!original.includes(eol)) {
+      original = original.replaceAll('\n', eol)
+    }
+    if (!ours.includes(eol)) {
+      ours = ours.replaceAll('\n', eol)
+    }
+  }
 
   // It is possible that the file has already been upgraded, in which case there is nothing to do
   if (theirs === ours) {