Use HTTPS in readme example

README.md

@@ -48,7 +48,7 @@ use isahc::prelude::*;
 fn main() -> Result<(), isahc::Error> {
     // Send a GET request and wait for the response headers.
     // Must be `mut` so we can read the response body.
-    let mut response = isahc::get("http://example.org")?;
+    let mut response = isahc::get("https://example.org")?;
 
     // Print some basic info about the response to standard output.
     println!("Status: {}", response.status());