Replace http://man7.org links with https://man7.org links.

I suspect the way http:// dies is that browsers just interpret it as
https:// anyway, but there's no reason not to just bulk fix all these at
source.

Change-Id: I38fa91728846d7c33207ef1bdadd4910eac9e941
diff --git a/libc/include/sys/file.h b/libc/include/sys/file.h
index ccdfeea..45117fa 100644
--- a/libc/include/sys/file.h
+++ b/libc/include/sys/file.h
@@ -41,7 +41,7 @@
 __BEGIN_DECLS
 
 /**
- * [flock(2)](http://man7.org/linux/man-pages/man2/flock.2.html) performs
+ * [flock(2)](https://man7.org/linux/man-pages/man2/flock.2.html) performs
  * advisory file lock operations.
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.