Use endOfLine: auto for prettier (#926)

On Windows, editors typically use CRLF by default. I don't see a reason
why we should be violating platform conventions, so just let anyone use
whatever (as long as it isn't mixed)

.prettierrc.json

@@ -1,3 +1,4 @@
 {
-  "trailingComma": "es5"
+  "trailingComma": "es5",
+  "endOfLine": "auto"
 }