Fix link to use https (#174)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 69eee2c..7670a41 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -189,7 +189,7 @@
 * Allow option values that look like options. This more closely matches the
   behavior of [`getopt`][getopt], the *de facto* standard for option parsing.
 
-[getopt]: http://man7.org/linux/man-pages/man3/getopt.3.html
+[getopt]: https://man7.org/linux/man-pages/man3/getopt.3.html
 
 ## 0.13.1