fix self signed certificate compatibility (#18)

Closes #17

Default keySize is 1024 and algorithm which is not enough nowadays.
Default algorithm is sha1 which is deprecated. https://security.googleblog.com/2014/09/gradually-sunsetting-sha-1.html

See https://github.com/jfromaniello/selfsigned/blob/c5ac42bdb5949bce47679221284331cab71a1e1e/README.md#options

Author: sonnyp

Diff for: README.md

@@ -215,6 +215,16 @@ To override a value, simply add it to `~/.chalet/conf.json` and run `chalet stop
 
 ## FAQ
 
+#### Problem with self signed certificates
+
+You will want to delete your existing certificates and restart chalet:
+
+```sh
+chalet stop
+rm ~/.chalet/cert.pem ~/.chalet/key.pem
+chalet start
+```
+
 #### Setting a fixed port
 
 ```sh

Diff for: src/daemon/pem.js

@@ -20,7 +20,9 @@ function generate() {
     const pems = selfsigned.generate(
       [{ name: "commonName", value: "chalet" }],
       {
-        days: 365
+        keySize: 2048,
+        days: 365,
+        algorithm: "sha256"
       }
     );
     fs.writeFileSync(KEY_FILE, pems.private, "utf-8");